[clang][builtin] Implement __builtin_allow_runtime_check (#87568)

RFC:
https://discourse.llvm.org/t/rfc-introduce-new-clang-builtin-builtin-allow-runtime-check/78281



---------

Co-authored-by: Noah Goldstein <goldstein.w.n@gmail.com>
Co-authored-by: Aaron Ballman <aaron@aaronballman.com>