[llvm] [AMDGPU] When allocating VGPRs, VGPR spills are not part of the prologue (PR #109439)

[Jay Foad via llvm-commits]

jayfoad wrote:

I don't know how to write a small test for this. The test case from #109294 is about 600K.

https://github.com/llvm/llvm-project/pull/109439