[llvm] [X86] Don't assume the FPCLASS category mask is a literal (PR #213171)

[Zane Hambly via llvm-commits]

Zaneham wrote:

Thanks @RKSimon, I am unable to merge this change so if you could that would be great. If there's anything else I need to do please let me know.

https://github.com/llvm/llvm-project/pull/213171