[ARM GlobalISel] Allow calls to varargs functions

Allow varargs functions to be called, both in arm and thumb mode. This
boils down to choosing the correct calling convention, which we can
easily test by making sure arm_aapcscc is used instead of
arm_aapcs_vfpcc when the callee is variadic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351424 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed