[clang] [llvm] [mlir] [AMDGPU] fix alignment of i128 (PR #213523)

[Matt Arsenault via cfe-commits]

arsenm wrote:

The datalayout default is bad, I think it should be changed to match the clang default (alternatively should fix the clang default, but the datalayout seems more wrong)

https://github.com/llvm/llvm-project/pull/213523