[llvm] [AMDGPU] Allow rematerialization of instructions with virtual register uses (PR #124327)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

Bring in https://github.com/llvm/llvm-project/pull/124366 to handle PhysReg uses in Remat candidates

allUsesAvailableAt essentially still ignores PhysReg uses, however, instructions with PhysReg uses are no longer viable RematCands so the liveness does not need to be checked.

https://github.com/llvm/llvm-project/pull/124327