GlobalISel: select G_VASTART on iOS AArch64.

The AAPCS ABI is substantially more complicated so that's coming in a separate
patch. For now we can generate correct code for iOS though.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294493 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed