Add IRBuilder routines for gc.statepoints, gc.results, and gc.relocates

Nothing particularly interesting, just adding infrastructure for use by in tree users and out of tree users.

Note: These were extracted out of a working frontend, but they have not been well tested in isolation.

Differential Revision: http://reviews.llvm.org/D6807



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224981 91177308-0d34-0410-b5e6-96231b3b80d8