Rename cfg_match! to cfg_select!

At [1] it was pointed out that `cfg_match!` syntax does not actually
align well with match syntax, which is a possible source of confusion.
The comment points out that usage is instead more similar to ecosystem
`select!` macros. Rename `cfg_match!` to `cfg_select!` to match this.

Tracking issue: https://github.com/rust-lang/rust/issues/115585

[1]: https://github.com/rust-lang/rust/issues/115585#issuecomment-2346307605

patches/0027-sysroot_tests-128bit-atomic-operations.patch

@@ -17,7 +17,7 @@ index 1e336bf..35e6f54 100644
 @@ -2,5 +2,4 @@
  // tidy-alphabetical-start
 -#![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
- #![cfg_attr(test, feature(cfg_match))]
+ #![cfg_attr(test, feature(cfg_select))]
  #![feature(alloc_layout_extra)]
  #![feature(array_chunks)]
 diff --git a/coretests/tests/atomic.rs b/coretests/tests/atomic.rs