A couple of small fixes to make core file debugging less noisy.
Don't want about being unable to find a needed objective-c runtime
function when we're core file debugging and can't jit anything
anyway.  Don't warn when quitting a debug session on a core file,
the program state can be reconstructed by re-running lldb on the
same core file again.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@181653 91177308-0d34-0410-b5e6-96231b3b80d8