[libc-commits] [libc] [libc] Some more MSVC compatibility in src/__support. (PR #158108)

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lntue wrote:

> So, MSVC does not have `__has_builtin`? I remember we used to have `LIBC_HAS_BUILTIN` as a workaround that returned zero if not. Maybe we need to bring that back. Every path should have a valid fallback so a lot of this should be automatic if we don't have the builtin.

The `__has_builtin` work around is still in `src/__support/config.h`.

https://github.com/llvm/llvm-project/pull/158108