[clang] [clang] [Headers] Don't use unreserved name in avx512fp16intrin.h (PR #98478)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> Hmm, what's your usage?
> 
> #define A
> 
> before
> 
> #include <avx512fp16intrin.h>
> 
> ?

Yes, exactly

https://github.com/llvm/llvm-project/pull/98478