[libc-commits] [libc] [libc] Move __LLVM_LIBC__ define to __llvm-libc-common.h (PR #126877)

[Joseph Huber via libc-commits]

jhuber6 wrote:

I'm okay with this, but including `features.h` and nothing else still needs to define this.

https://github.com/llvm/llvm-project/pull/126877