[llvm] [AMDGPU] Add legality check when folding short 64-bit literals (PR #69391)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

I tend to believe this is not exploitable because we do not select these moves. But better be safe than sorry. Especially given that it will ultimately result in the selection of such literals into a single move.

https://github.com/llvm/llvm-project/pull/69391