[clang] [compiler-rt] [llvm] [X86] Support APXF to enable __builtin_cpu_supports. (PR #80636)

[Freddy Ye via cfe-commits]

FreddyLeaf wrote:

After [fa42b33](https://github.com/llvm/llvm-project/pull/80636/commits/fa42b33d62227bd88cc5d63431244d0caac1e286)
1. An error will be thrown out if compiling `__builtin_cpu_supports("egpr")`
2. __attribute__((__target__("apxf"))) is not supported in this patch, no matter amend features or FMV.
3. __attribute__((__target__("egpr,cf"))) is already supported before this PR.

I think 3rd can be a workaround of 2nd, and gcc also hasn't supported FMV for "apxf".

https://github.com/llvm/llvm-project/pull/80636