[clang] [llvm] Remove mmx 3dnow (PR #96246)

[Craig Topper via cfe-commits]

topperc wrote:

Was `3dnow` never part of `sys:getHostCPUFeatures` for -march=native? I expected you would need to remove it from there, but it looks like it isn't there

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