GlobalISel: legalize va_arg on AArch64.

Uses a Custom implementation because the slot sizes being a multiple of the
pointer size isn't really universal, even for the architectures that do have a
simple "void *" va_list.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295255 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed