SuccIterator on bbs without terminator insts

SuccIterator on bbs without terminator insts

Remove the assert that triggers if SuccIterator is constructed for a basic block
without a terminator instruction. Instead of triggering an assert a succ_end()
iterator is returned. This models a basic block with zero successors and allows
us to use F->viewCFG() on incompletely constructed functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134398 91177308-0d34-0410-b5e6-96231b3b80d8