[compiler-rt] [compiler-rt] Fix test ifdefs and XFAILs (PR #160687)

[David Spickett via llvm-commits]

DavidSpickett wrote:

The code is new to me but after inspecting the headers, the change makes sense.

I'll let @ahatanak take a look too.

https://github.com/llvm/llvm-project/pull/160687