[libc-commits] [libc] [libc] Move LLVM_LIBC_IS_DEFINED macro to its own header (PR #190081)

[Petr Hosek via libc-commits]

https://github.com/petrhosek requested changes to this pull request.

The new headers need to be included in https://github.com/llvm/llvm-project/blob/main/libc/src/__support/macros/CMakeLists.txt and all users of the new headers need corresponding dependencies.

https://github.com/llvm/llvm-project/pull/190081