Add missing unsafe {} blocks in const thread_local! impl

These are only necessary when the user of thread_local! uses
`#![deny(unsafe_op_in_unsafe_fn)]`

Author: bjorn3

library/std/src/thread/local.rs

@@ -189,7 +189,11 @@ macro_rules! __thread_local_inner {
             #[cfg(all(target_family = "wasm", not(target_feature = "atomics")))]
             {
                 static mut VAL: $t = INIT_EXPR;
-                Some(&VAL)
+                // FIXME: remove the #[allow(...)] marker when macros don't
+                // raise warning for missing/extraneous unsafe blocks anymore.
+                // See https://github.com/rust-lang/rust/issues/74838.
+                #[allow(unused_unsafe)]
+                unsafe { Some(&VAL) }
             }
 
             // If the platform has support for `#[thread_local]`, use it.
@@ -205,7 +209,13 @@ macro_rules! __thread_local_inner {
                 // just get going.
                 if !$crate::mem::needs_drop::<$t>() {
                     unsafe {
-                        return Some(&VAL)
+                        // FIXME: remove the #[allow(...)] marker when macros don't
+                        // raise warning for missing/extraneous unsafe blocks anymore.
+                        // See https://github.com/rust-lang/rust/issues/74838.
+                        #[allow(unused_unsafe)]
+                        unsafe {
+                            return Some(&VAL);
+                        }
                     }
                 }