[compiler-rt] [compiler-rt] Stop using x86 builtin on AArch64 with GCC (PR #93890)

[Simon Tatham via llvm-commits]

statham-arm wrote:

I enjoy a good piece of C macro trickery :slightly_smiling_face: but in this case I agree that it doesn't really save anything, because you've got to make sure all the affected builtins are listed at the top of the file.

Also, I don't want to make you go and fix every case of this in the whole of LLVM just to get the one immediate problem fixed!

I think it's a reasonable stopping point to just fix the two similar cases in this file in the same way. Otherwise someone seeing them right next to each other might think they were _deliberately_ opposite ways round, and wonder why.

https://github.com/llvm/llvm-project/pull/93890