[llvm] [X86][NewPM] Fill out X86CodeGenPassBuilder (PR #176061)

[Alan Zhao via llvm-commits]

alanzhao1 wrote:

If I had to guess it's because the [symbol in question is `static`](https://github.com/llvm/llvm-project/blob/7f2eb314cd4837f4f4cff4d3c529aee140c49ea2/llvm/lib/Target/X86/X86TargetMachine.cpp#L56-L58)

But I'm still confused because the `Release` builds still work...

https://github.com/llvm/llvm-project/pull/176061