[llvm] [SPIR-V] Add pass to fixup global variable AS (PR #124591)

[Michal Paszkowski via llvm-commits]

https://github.com/michalpaszkowski commented:

Left a couple of comments. I think the proposal makes sense and the pass looks good, could not find any discrepancies or think of any additional things worth considering.

The note on the 65536 limit made me think that we should probably add some error handling considering ID allocation constraints in the backend for such extreme cases (although not in this pass).

https://github.com/llvm/llvm-project/pull/124591