[clang] [Clang][HIP] Deprecate the AMDGCN_WAVEFRONT_SIZE macros (PR #112849)

[Fabian Ritter via cfe-commits]

ritter-x2a wrote:

> > Just a heads up, this change is gonna break some OpenMP tests, specifically those prefix with `ompx`.
> 
> Just to clarify, adding the deprecation warning will break them, or the eventual, as-of-yet not-scheduled, removal, will?

On my system, the deprecation warning did not break any lit tests (nor tests from our internal testing). The `ompx` tests use the macro and will break once we actually remove it.

https://github.com/llvm/llvm-project/pull/112849