[libc-commits] [libc] [libc] Fix problem with older compilers that do not have __has_builtin. (PR #150264)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 approved this pull request.

We removed this earlier as a cleanup because it was decided that all supported compilers had the builtins we use. However, as more of the `libc` interface gets exported to `libc` (clang, libc++, offload) will will need to keep this compatible with the minimum supported GCC for those exported functions. LG.

https://github.com/llvm/llvm-project/pull/150264