[clang] [llvm] [LLVM] Fix incorrect alignment on AMDGPU variadics (PR #96370)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Here, because the minimum alignment is 4, we will only increment the
buffer by 4, 

It should be incrementing by the size? 4 byte aligned access of 8 byte type should work fine

https://github.com/llvm/llvm-project/pull/96370