Rollup merge of #99332 - jyn514:stabilize-label-break-value, r=petrochenkov

Stabilize `#![feature(label_break_value)]`

See the stabilization report in rust-lang/rust#48594 (comment).

Author: JohnTitor

std/src/lib.rs

@@ -252,7 +252,7 @@
 #![feature(dropck_eyepatch)]
 #![feature(exhaustive_patterns)]
 #![feature(intra_doc_pointers)]
-#![feature(label_break_value)]
+#![cfg_attr(bootstrap, feature(label_break_value))]
 #![feature(lang_items)]
 #![feature(let_else)]
 #![feature(linkage)]