[llvm-branch-commits] [SPIRV][NewPM] Port SPIRVPostLegalizer (PR #219109)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/219109

Standard NewPM pass porting. Most of the implementation was already in
static functions so this was pretty simple.