[clang] [NVPTX][AMDGPU][CodeGen] Fix `local_space nullptr` handling for NVPTX and local/private `nullptr` value for AMDGPU. (PR #78759)

[Artem Belevich via cfe-commits]

https://github.com/Artem-B commented:

It would be great to add some tests for local AS null pointers for NVPTX and AMDGPU back-ends.


https://github.com/llvm/llvm-project/pull/78759