Fix rust-lang#124478 - offset_of! returns a temporary

This was due to the must_use() call. Adding HIR's OffsetOf to the must_use
checking within the compiler avoids this issue.

Author: GKFX

Diff for: core/src/mem/mod.rs

@@ -1340,8 +1340,8 @@ impl<T> SizedTypeProperties for T {}
 /// assert_eq!(mem::offset_of!(Option<&u8>, Some.0), 0);
 /// ```
 #[stable(feature = "offset_of", since = "1.77.0")]
-#[allow_internal_unstable(builtin_syntax, hint_must_use)]
+#[allow_internal_unstable(builtin_syntax)]
 pub macro offset_of($Container:ty, $($fields:expr)+ $(,)?) {
     // The `{}` is for better error messages
-    crate::hint::must_use({builtin # offset_of($Container, $($fields)+)})
+    {builtin # offset_of($Container, $($fields)+)}
 }