[clang] [cuda][[HIP] `__constant__` should imply constant (PR #110182)

[Artem Belevich via cfe-commits]

Artem-B wrote:

Well, it's certainly used that way in existing CUDA code and it's been around forever: 
Here are few random examples from both 10 years ago:
https://stackoverflow.com/questions/20535683/cuda-5-5-cudamemcpytosymbol-constant-and-out-of-scope-error
and a fairly recent example: https://forums.developer.nvidia.com/t/constant-memory-cudamemcpytosymbol-and-compilation-units/248780


https://github.com/llvm/llvm-project/pull/110182