[compiler-rt] compiler-rt: Stop using APPLE cmake variable (PR #203357)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> I think there's an issue here with !LLVM_ENABLE_PER_TARGET_RUNTIME_DIR

Yeah, APPLE targets turn that off / cannot support it for reasons unknown to me.

https://github.com/llvm/llvm-project/pull/203357