[llvm] [X86] Run X86FastPreTileConfigPass only with FastISel. (PR #70754)

[Evgenii Kudriashov via llvm-commits]

e-kud wrote:

> This is not the kind of problem that can be correctly solved by changing the pass set. The MIR must follow a consistent set of rules at all points. All selectors must be bound to emit MIR that respects the rules. Shuffling around which passes run with which selector is expected will not work reliably, especially with fallbacks. Every selector should be guaranteeing no virtual registers without classes are passed through

Agreed. Also I've realized that generally we want to keep this pass for GlobalISel as it allows a fast skip at O0. Closing in favor of the original issue that leaves registers without classes.

https://github.com/llvm/llvm-project/pull/70754