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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

This was the original behavior of my patch, but I reverted it because it broke all the HIP headers that were unintentionally relying on this. Has that been resolved?

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