Revert 4 last AMDGPU commits to unbreak Windows bots

Revert "AMDGPU: Try to fix build error with old gcc"
This reverts commit c7ad12d0.

Revert "AMDGPU: Use umin in set.rounding expansion"
This reverts commit a56f0b51.

Revert "AMDGPU: Optimize set_rounding if input is known to fit in 2 bits (#88588)"
This reverts commit b4e751e2.

Revert "AMDGPU: Implement llvm.set.rounding (#88587)"
This reverts commit 9731b77e.