Resolve unexpected_cfgs warning

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/mod.rs:31:7
       |
    31 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: expected names are: `clippy`, `debug_assertions`, `doc`, `docsrs`, `doctest`, `feature`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `test`, `ub_checks`, `unix`, `windows`
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration
       = note: `#[warn(unexpected_cfgs)]` on by default

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/mod.rs:34:7
       |
    34 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
     --> src/lexical/large_powers.rs:5:7
      |
    5 | #[cfg(limb_width_32)]
      |       ^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
     --> src/lexical/large_powers.rs:8:7
      |
    8 | #[cfg(limb_width_64)]
      |       ^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/math.rs:40:7
       |
    40 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/math.rs:43:7
       |
    43 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/math.rs:46:7
       |
    46 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/math.rs:49:7
       |
    49 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/math.rs:53:7
       |
    53 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/math.rs:56:7
       |
    56 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/math.rs:59:7
       |
    59 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/math.rs:62:7
       |
    62 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/math.rs:82:7
       |
    82 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/math.rs:89:7
       |
    89 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
     --> src/lexical/small_powers.rs:6:7
      |
    6 | #[cfg(limb_width_32)]
      |       ^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> src/lexical/small_powers.rs:12:7
       |
    12 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> src/lexical/small_powers.rs:18:7
       |
    18 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/mod.rs:31:7
       |
    31 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: expected names are: `clippy`, `debug_assertions`, `doc`, `docsrs`, `doctest`, `feature`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `test`, `ub_checks`, `unix`, `windows`
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration
       = note: `#[warn(unexpected_cfgs)]` on by default

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/mod.rs:34:7
       |
    34 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
     --> tests/../src/lexical/large_powers.rs:5:7
      |
    5 | #[cfg(limb_width_32)]
      |       ^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
     --> tests/../src/lexical/large_powers.rs:8:7
      |
    8 | #[cfg(limb_width_64)]
      |       ^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/math.rs:40:7
       |
    40 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/math.rs:43:7
       |
    43 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/math.rs:46:7
       |
    46 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/math.rs:49:7
       |
    49 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/math.rs:53:7
       |
    53 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/math.rs:56:7
       |
    56 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/math.rs:59:7
       |
    59 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/math.rs:62:7
       |
    62 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/math.rs:82:7
       |
    82 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/math.rs:89:7
       |
    89 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
     --> tests/../src/lexical/small_powers.rs:6:7
      |
    6 | #[cfg(limb_width_32)]
      |       ^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/../src/lexical/small_powers.rs:12:7
       |
    12 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/../src/lexical/small_powers.rs:18:7
       |
    18 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_32`
      --> tests/lexical/math.rs:21:7
       |
    21 | #[cfg(limb_width_32)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_32)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `limb_width_64`
      --> tests/lexical/math.rs:26:7
       |
    26 | #[cfg(limb_width_64)]
       |       ^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(limb_width_64)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

build.rs

@@ -3,6 +3,9 @@ use std::env;
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
 
+    println!("cargo:rustc-check-cfg=cfg(limb_width_32)");
+    println!("cargo:rustc-check-cfg=cfg(limb_width_64)");
+
     // Decide ideal limb width for arithmetic in the float parser. Refer to
     // src/lexical/math.rs for where this has an effect.
     let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();