[FastISel] Factor out stackmap intrinsic selection code into a dedicated helper method. NFCI.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212140 91177308-0d34-0410-b5e6-96231b3b80d8
Run clang-format on llvm-size.cpp to tidy things up. No functional changes.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212141 91177308-0d34-0410-b5e6-96231b3b80d8