[AArch64] Use CHECK-LABEL in ARM64 ABI unit tests.
[FastIsel][AArch64] Add support for the FastLowerCall and FastLowerIntrinsicCall target-hooks.

This commit modifies the existing call lowering functions to be used as the
FastLowerCall and FastLowerIntrinsicCall target-hooks instead.

This enables patchpoint intrinsic lowering for AArch64.

This fixes <rdar://problem/17733076>
XFAIL the test on MIPS

Not sure how to debug this one without a MIPS machine. Any takers?