[clang] [AMDGPU] Do not emit arch dependent macros with unspecified cpu (PR #80035)

[Joseph Huber via cfe-commits]

================
@@ -175,6 +175,8 @@ Predefined Macros
      - Defined when the GPU default stream is set to per-thread mode.
    * - ``HIP_API_PER_THREAD_DEFAULT_STREAM``
      - Alias to ``__HIP_API_PER_THREAD_DEFAULT_STREAM__``. Deprecated.
+   * - ``__AMDGCN_WAVEFRONT_SIZE__``
----------------
jhuber6 wrote:

Tried to explain this further.

https://github.com/llvm/llvm-project/pull/80035