[clang] clang/HIP: Remove some unused ocml function declarations (PR #204735)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> Hello! Some of the removed the functions are still used by amd_hip_fb16.h (https://github.com/ROCm/clr/blob/amd-staging/hipamd/include/hip/amd_detail/amd_hip_fp16.h) e.g `__ocml_sin_2f16(x), __ocml_cos_2f16(x), __ocml_sqrt_2f16(x)` which our downstream HIP testing depends on.
> 
> Do we have plan to update amd_hip_fp16.h accordingly, what is the best way to mitigate this? Thanks!
> 
> cc: @jplehr

The HIP headers have their own declarations for the used symbols device_library_decls.h, it cannot rely on the external provided declarations. If you're using the symbols there, you have to do your own declare. Long term all the ocml direct references in the hip headers should be removed 

https://github.com/llvm/llvm-project/pull/204735