[llvm] [AMDGPU][GlobalISel] Fix issue with copy_scc_vcc on gfx7 (PR #165355)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Also could we do the OR on newer targets also?

Won't that waste an SGPR in some cases, since we need to allocate one for the dead dest of the OR?

https://github.com/llvm/llvm-project/pull/165355