Disable assert_unsafe_precondition to measure compile-time cost

Author: saethlin

Diff for: library/core/src/ub_checks.rs

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