[llvm] [SPIRV] Add support for pointers to functions with aggregate args/returns as global variables / constant initialisers (PR #169595)

[Alex Voicu via llvm-commits]

https://github.com/AlexVlx commented:

> Just an idea: Could we use `ValueAsMetadata` in here instead of the name? 

Potentially, but I wanted to more or less retain the existing code / minimise "innovation", so I didn't think profoundly re-factoring in this change:)

https://github.com/llvm/llvm-project/pull/169595