Auto merge of rust-lang#123679 - saethlin:measure-ub-checks, r=<try>

Disable assert_unsafe_precondition to measure compile-time cost

r? ghost

Author: bors

library/core/src/ub_checks.rs

@@ -69,6 +69,7 @@ macro_rules! assert_unsafe_precondition {
                 }
             }
 
+            #[cfg(debug_assertions)]
             if ::core::ub_checks::$kind() {
                 precondition_check($($arg,)*);
             }