[clang] [Clang][SPIRV][AMDGPU] Override `supportsLibCall` for AMDGCNSPIRV (PR #143814)

[Alex Voicu via cfe-commits]

https://github.com/AlexVlx commented:

#143431 is related to this, but it proposes a more pervasive change, which would require further discussion and clarification around what the SPIR-V BE wants to do / support in term of libcalls.

https://github.com/llvm/llvm-project/pull/143814