GlobalISel: support translating va_arg

Since (say) i128 and [16 x i8] map to the same type in generic MIR, we also
need to attach the required alignment info.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295254 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed