Use faster thread_local! init where possible

Author: kornelski

library/std/src/io/stdio.rs

@@ -20,7 +20,7 @@ type LocalStream = Arc<Mutex<Vec<u8>>>;
 
 thread_local! {
     /// Used by the test crate to capture the output of the print macros and panics.
-    static OUTPUT_CAPTURE: Cell<Option<LocalStream>> = {
+    static OUTPUT_CAPTURE: Cell<Option<LocalStream>> = const {
         Cell::new(None)
     }
 }

library/std/src/sync/mpmc/waker.rs

@@ -204,6 +204,6 @@ impl Drop for SyncWaker {
 pub fn current_thread_id() -> usize {
     // `u8` is not drop so this variable will be available during thread destruction,
     // whereas `thread::current()` would not be
-    thread_local! { static DUMMY: u8 = 0 }
+    thread_local! { static DUMMY: u8 = const { 0 } }
     DUMMY.with(|x| (x as *const u8).addr())
 }