[llvm] [AIX] Handle arbitrary sized integers when lowering formal arguments passed on the stack (PR #149351)

[Amy Kwan via llvm-commits]

amy-kwan wrote:

Ideally, we would like this in LLVM 21 if possible (forgot to set the milestone)

/cherry-pick f48a8da34292b367ba8a5e7b25065172df966848

https://github.com/llvm/llvm-project/pull/149351