[llvm] [SystemZ] Add a SystemZ specific pre-RA scheduling strategy. (PR #135076)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

Did another experiment by removing the extra check that puts two SUs that both have a PRegBias in their source order relative to each other. This still seems possibly useful - one regression around 1% seen, otherwise no changes.

https://github.com/llvm/llvm-project/pull/135076