[clang] [clang][AMDGPU] Don't define feature macros on host code (PR #83558)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

in HIP headers, warpSize is defined with __AMDGCN_WAVEFRONT_SIZE and there are a bunch of uses of __AMDGCN_WAVEFRONT_SIZE or warpSize as constants:

https://github.com/search?q=repo%3AROCm%2Fclr%20__AMDGCN_WAVEFRONT_SIZE&type=code

These can be fixed relatively easily by conditioning them for device compilation only and only declare those device functions for host compilation. However, the difficult part is HIP apps that uses warpSize as constants. They all need to make similar changes. In the case of rocprim, that is non-trivial.

https://github.com/llvm/llvm-project/pull/83558