[clang] [X86][Headers] Specify result of NaN comparisons (PR #85862)

[Paul T Robinson via cfe-commits]

pogo59 wrote:

cc @craigflores

I have resisted the temptation to do a general editorial pass over these headers. This patch is "functional" in that it (mostly) adds information that was not provided before. There's a lot that could be done to make the descriptions more consistent with each other but I'll save that for another "nonfunctional" patch. The one editorial thing I did this time around was replace "yields" with "returns" since I was often touching those sentences anyway.

https://github.com/llvm/llvm-project/pull/85862