Teach the LLParser to fail gracefully when it encounters an invalid label name.

Previous it would either assert in +Asserts, or crash in -Asserts. Found by fuzzing LLParser.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230935 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed