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

[Matt Arsenault via llvm-commits]

arsenm 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 

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