[clang] [Clang][AMDGPU] Name the builtin in required target feature diagnostics (PR #218358)

[Shilei Tian via cfe-commits]

https://github.com/shiltian requested changes to this pull request.

First of all, AMDGPU should not have dedicated target feature check in the first place. Second, this is a generic improvement that should go to the generic handling.

https://github.com/llvm/llvm-project/pull/218358