[llvm] [AMDGPU] Use absolute relocations when compiling for AMDPAL and Mesa3D (PR #67791)

[Thomas Symalla via llvm-commits]

tsymalla wrote:

I agree with your understanding. The idea of using buildCast was that it boils down to a COPY if it can, but does some smartness in other cases. The code should only create new registers when the dest has a register class, and since sometimes we have a register (Si_cc_gfx_ret) where the data is stored in sgprs but the type is pointer, this should work as well (which will not work with sole COPY afaik). At least that’s what I experienced during my tests.

https://github.com/llvm/llvm-project/pull/67791