Add a new -a / --address argument to image show-unwind to get the
unwind instructions for a function/symbol which contains that
address.

Update the unwind_diagnose.py script to use this instead of doing
image show-unwind by name to avoid cases where there are multiple
name definitions.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@180079 91177308-0d34-0410-b5e6-96231b3b80d8