Auto merge of rust-lang#94738 - Urgau:rustbuild-check-cfg-values, r=Mark-Simulacrum

Enable conditional checking of values in the Rust codebase

This pull-request enable conditional checking of (well known) values in the Rust codebase.

Well known values were added in rust-lang#94362. All the `target_*` values are taken from all the built-in targets which is why some extra values were needed do be added as they are not (yet ?) defined in any built-in targets.

r? `@Mark-Simulacrum`

Author: bors

core/tests/iter/adapters/step_by.rs

@@ -50,8 +50,6 @@ fn test_iterator_step_by_nth() {
 
 #[test]
 fn test_iterator_step_by_nth_overflow() {
-    #[cfg(target_pointer_width = "8")]
-    type Bigger = u16;
     #[cfg(target_pointer_width = "16")]
     type Bigger = u32;
     #[cfg(target_pointer_width = "32")]