Alow static_mut_refs with rustc-dep-of-std

This combination raises an error suggesting `&raw mut errno`. This was
removed in 1.0, but allow the lint on 0.2 for now.

src/lib.rs

@@ -22,6 +22,8 @@
 #![cfg_attr(feature = "rustc-dep-of-std", feature(link_cfg, no_core))]
 #![cfg_attr(libc_thread_local, feature(thread_local))]
 #![cfg_attr(feature = "rustc-dep-of-std", allow(internal_features))]
+// DIFF(1.0): The thread local references that raise this lint were removed in 1.0
+#![cfg_attr(feature = "rustc-dep-of-std", allow(static_mut_refs))]
 // Enable extra lints:
 #![cfg_attr(feature = "extra_traits", deny(missing_debug_implementations))]
 #![deny(missing_copy_implementations, safe_packed_borrows)]