More diagnostic items for Clippy usage

This adds a couple of more diagnostic items to be used in Clippy.
I chose these particular ones because they were the types which we seem
to check for the most in Clippy. I'm not sure if the
`cfg_attr(not(test))` is needed, but it was also used for `Vec` and a
few other types.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index 0cb16b19d73..797b22fdd12 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -108,6 +108,7 @@ use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
 /// *guard += 1;
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "mutex_type")]
 pub struct Mutex<T: ?Sized> {
     // Note that this mutex is in a *box*, not inlined into the struct itself.
     // Once a native mutex has been used once, its address can never change (it