[clang] [llvm] [OpenMP] Use generic IR for the OpenMP DeviceRTL (PR #119091)

[Shilei Tian via cfe-commits]

shiltian wrote:

> > I like this method, but just out of curiosity, did we use anything in AMDGPU implementation that has target dependent lowering in the front end? If not, this is totally fine I'd say.
> 
> We used to use the `__AMDGCN_WAVEFRONT_SIZE` but that was removed for unrelated reasons.

And now we don't have any target specific part in AMDGPU implementation? Quite surprised but happy to hear that.

https://github.com/llvm/llvm-project/pull/119091