Revamp how debugging information is emitted for debug info objects.

Revamp how debugging information is emitted for debug info objects.

It's not necessary for each DI class to have its own copy of `print' and
`dump'. Instead, just give DIDescriptor those methods and have it call the
appropriate debugging printing routine based on the type of the debug
information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159237 91177308-0d34-0410-b5e6-96231b3b80d8