[llvm] X86: Avoid using isArch64Bit for 64-bit checks (PR #157412)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > We have x86_64 analogues in downstream code. It will make code complicated to check a couple of them each time.
> 
> Then there should be an isX86_64 helper in Triple like other targets do

Are you intending to handle this or shall one of us?

https://github.com/llvm/llvm-project/pull/157412