Rollup merge of #117556 - obeis:static-mut-ref-lint, r=davidtwco

Disallow reference to `static mut` and adding `static_mut_ref` lint

Closes #114447

r? `@scottmcm`

example/mini_core_hello_world.rs

@@ -111,6 +111,9 @@ fn start<T: Termination + 'static>(
 }
 
 static mut NUM: u8 = 6 * 7;
+
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
+#[allow(static_mut_ref)]
 static NUM_REF: &'static u8 = unsafe { &NUM };
 
 unsafe fn zeroed<T>() -> T {