[clang] [llvm] Remove support for 3DNow!, both intrinsics and builtins. (PR #96246)

[Ian Anderson via cfe-commits]

ian-twilightcoder wrote:

> Do the include guard macros make it problematic to expose as a textual header? I would not have thought that to be the case.

It means that the header guard declaration would be compiled into every pcm that includes the header. Which is maybe fine for this one, but generally isn't good.

https://github.com/llvm/llvm-project/pull/96246