[clang] [OpenMP][clang][HIP][CUDA] fix weak alias emit on device compilation (PR #164326)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

can we add a section "Alias Attribute Support" to https://clang.llvm.org/docs/HIPSupport.html, briefly describe the usecase of alias attribute in HIP with some examples?

https://github.com/llvm/llvm-project/pull/164326