[compiler-rt] [compiler-rt] Explicitly enable C extensions for profile (PR #110555)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo commented:

What happens here, if running on a version of CMake that doesn't support the new policy and then probably doesn't support the `<LANG>_EXTENSIONS` target property?

https://github.com/llvm/llvm-project/pull/110555