This patch implements clang support for the ACLE special register intrinsics

in section 10.1, __arm_{w,r}sr{,p,64}.

This includes arm_acle.h definitions with builtins and codegen to support
these, the intrinsics are implemented by generating read/write_register calls
which get appropriately lowered in the backend based on the register string
provided. SemaChecking is also implemented to fault invalid parameters.

Differential Revision: http://reviews.llvm.org/D9697

llvm-svn: 239737