[llvm] [AMDGPU] Include WWM register spill into BB Prolog (PR #111496)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Adding any VGPR reload to the prologue will take us back to the SplitKit assert issue. Since WWM VGPR reload creates a new live interval in the VGPR it defines, we end up at the same point where we started.

I think the register allocation split avoids this. The WWM spills and VGPR spills do not coexist anymore. The 3rd run of the allocator will see the lowered WWM spills 

https://github.com/llvm/llvm-project/pull/111496