[FastISel] Add target-independent patchpoint intrinsic support. WIP.

This implements the target-independent lowering for the patchpoint
intrinsic. Targets have to implement the FastLowerCall
hook to support this intrinsic.

Related to <rdar://problem/17427052>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212849 91177308-0d34-0410-b5e6-96231b3b80d8