Enable build with global-context-less-secure

All features should be able to be built individually, this is currently
not the case with `global-context-less-secure`.

Enable `std` if `global-context-less-secure` is enabled (because `Once`
only comes from `std`, not available in `core`).

Add `global-context-less-secure` to the features test array in
`contrib/test.sh`.

Cargo.toml

@@ -27,7 +27,7 @@ rand-std = ["rand/std"]
 recovery = ["secp256k1-sys/recovery"]
 lowmemory = ["secp256k1-sys/lowmemory"]
 global-context = ["std", "rand-std", "global-context-less-secure"]
-global-context-less-secure = []
+global-context-less-secure = ["std"]
 
 [dependencies]
 secp256k1-sys = { version = "0.4.2", default-features = false, path = "./secp256k1-sys" }

contrib/test.sh

@@ -1,6 +1,6 @@
 #!/bin/sh -ex
 
-FEATURES="bitcoin_hashes global-context lowmemory rand rand-std recovery serde"
+FEATURES="bitcoin_hashes global-context-less-secure global-context lowmemory rand rand-std recovery serde"
 
 # Use toolchain if explicitly specified
 if [ -n "$TOOLCHAIN" ]

src/context.rs

@@ -10,13 +10,13 @@ use Secp256k1;
 pub use self::alloc_only::*;
 
 #[cfg(feature = "global-context-less-secure")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "global-context", feature = "global-context-less-secure"))))]
+#[cfg_attr(docsrs, doc(cfg(feature = "global-context-less-secure")))]
 /// Module implementing a singleton pattern for a global `Secp256k1` context
 pub mod global {
     #[cfg(feature = "global-context")]
     use rand;
 
-    use std::ops::Deref;
+    use core::ops::Deref;
     use std::sync::Once;
     use {Secp256k1, All};