Bad interaction of RUSTFLAGS and cargo miri

[RalfJung]

Running RUSTFLAGS=-g cargo miri run does not work:

error: -g and -C debuginfo both provided

error: Could not compile `byteorder`.

Adding some debug printing shows that we are running the command

"rustc" "-Zalways-encode-mir" "-Zmir-emit-retag" "-Zmir-opt-level=0" "--crate-name" "byteorder" "/home/r/.cargo/registry/src/github.com-1ecc6299db9ec823/byteorder-1.0.0/src/lib.rs" "--color" "always" "--crate-type" "lib" "--emit=dep-info,link" "-C" "debuginfo=2" "--cfg" "feature=\"default\"" "--cfg" "feature=\"std\"" "-C" "metadata=96f138114898c6b9" "-C" "extra-filename=-96f138114898c6b9" "--out-dir" "/home/r/src/rust/miri.2/test-cargo-miri/target/debug/deps" "-L" "dependency=/home/r/src/rust/miri.2/test-cargo-miri/target/debug/deps" "--cap-lints" "allow" "-g" "--sysroot" "/home/r/.cache/miri/HOST" "--cfg" "feature=\"cargo-miri\""

this, indeed, contains both -g and -C debuginfo.

[RalfJung]

Fixed by rust-lang/rust#60426