[AArch64] Implement GHC calling convention

Original patch by Luke Iannini.  Minor improvements and test added by
Erik de Castro Lopo.

Differential Revision: http://reviews.llvm.org/D6877

From: Erik de Castro Lopo <erikd@mega-nerd.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226473 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed