[clang] [libc] [llvm] Reapply "[AMDGPU] Use COV6 by default (#118515)" (PR #130963)

[Shilei Tian via llvm-commits]

shiltian wrote:

> > The OpenMP runtime doesn't know how to handle `generic` ISAs right?
> 
> I don't understand why that is tied to the version

It is probably no longer tied to the version since we no longer build one device runtime per target.

https://github.com/llvm/llvm-project/pull/130963