Delete the BasicBlock ctor that only takes a BasicBlock to insert before. This

Delete the BasicBlock ctor that only takes a BasicBlock to insert before.  This
fails when the basic block points to the function->end.  Instead, require that
the client pass in the function AND the basicblock to insert into.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11112 91177308-0d34-0410-b5e6-96231b3b80d8