[FastISel] Add support for the stackmap intrinsic.

This implements target-independent FastISel lowering for the stackmap intrinsic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210742 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Improve frameaddress test from r210709.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210743 91177308-0d34-0410-b5e6-96231b3b80d8