Fix LLVM vs Apple LLVM version numbering confusion, for $avx512ifma

Fix LLVM vs Apple LLVM version numbering confusion, for $avx512ifma

Apple LLVM has a different version numbering scheme than upstream LLVM.
That makes for quite a bit of confusion.

https://en.wikipedia.org/wiki/Xcode#Toolchain_versions to the rescue,
they have collected quite a lot of useful data.

This change is concentrated around the `$avx512ifma` flag

Fixes #16670 for OpenSSL 3.0

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19352)