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

[James Y Knight via cfe-commits]

jyknight wrote:

I've written down an overall plan into issue #98272. I'm not sure if everything can be finished by the LLVM 19 branch date, but I don't think there's any reason to wait on this CL. I'd like to just go ahead with it.

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