[llvm] [RegAlloc] Remove default restriction on non-trivial rematerialization (PR #159211)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

A couple of points for later reference:
* As the compile time concern reported against https://reviews.llvm.org/D106408 was never identified (i.e. no reproducer shared), we may see a regression on some workloads after this lands.  Please do not revert unless a reproducer is available!  I have a rough idea of the possible cause, but need a reproducer to confirm a fix.\
* If for some reason this doesn't stick, we will probably move to enabling this selectively by target.  AMDGPU already does this.  RISC-V allows a couple specific cases, and we do want this more broadly.  

https://github.com/llvm/llvm-project/pull/159211