This removes CreateMalloc from CallInst and adds it to the IRBuilderBase class.
We no longer needed the Instruction *InsertBefore and
BasicBlock *InsertAtEnd arguments of the createMalloc helper
function because we're using IRBuilder now. That's why I we also don't
need 4 CreateMalloc functions, but only two.
@nikic I wonder if I should have kept this. I don't know no *.mli files if this was a binding to CallInst::CreateMalloc, then it should go I think.