Add #[deny(unsafe_op_in_unsafe_fn)] to thread_local!(const).

This avoids 'unused unsafe' warnings when using this feature inside std.

library/std/src/thread/local.rs

@@ -179,6 +179,7 @@ macro_rules! __thread_local_inner {
     // used to generate the `LocalKey` value for const-initialized thread locals
     (@key $t:ty, const $init:expr) => {{
         #[cfg_attr(not(windows), inline(always))] // see comments below
+        #[deny(unsafe_op_in_unsafe_fn)]
         unsafe fn __getit(
             _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
         ) -> $crate::option::Option<&'static $t> {