[PATCH] Enable invoking the patchpoint intrinsic

[Kevin Modzelewski]

Ok, I rebased onto trunk.  One thing I failed to mention is that this patch depends on another that I sent out, D5657, since I wanted to separate some refactoring changes from the actual invoke-supporting change.

I switched from a CallInst to an ImmutableCallSite since these functions can now take either a CallInst or an InvokeInst (specifically, visitPatchpoint can now be called from both visitIntrinsicCall and from visitInvoke), and my understanding was that an (Immutable)CallSite is the preferred way to support both.  Happy to do it some other way, though.

http://reviews.llvm.org/D5634