[clang] [Headers][X86] Add macro descriptions to ia32intrin.h (PR #78613)

[Paul T Robinson via cfe-commits]

pogo59 wrote:

> When a macro is merely an alternate name for an intrinsic function, does it want to be documented as its own intrinsic function? I assume yes in this patch, but if there's a different tactic that avoids duplicating a bunch of descriptions, I'm open to suggestions.

I discovered the \see directive and added those.

https://github.com/llvm/llvm-project/pull/78613