[IRBuilder] Add a CreateGCStatepointInvoke.

[IRBuilder] Add a CreateGCStatepointInvoke.

Renames the original CreateGCStatepoint to CreateGCStatepointCall, and
moves invoke creating functionality from PlaceSafepoints.cpp to
IRBuilder.cpp.

This changes the labels generated for PlaceSafepoints/invokes.ll so use
a regex there to make the basic block labels more resilient.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236672 91177308-0d34-0410-b5e6-96231b3b80d8