Modify behavior of -ast-dump-lookups: if -ast-dump is not also provided, dump

Modify behavior of -ast-dump-lookups: if -ast-dump is not also provided, dump
anyway. If -ast-dump *is* also provided, then dump the AST declarations as well
as the lookup results. This is invaluable for cross-correlating the lookup
information with the declarations actually found.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@215393 91177308-0d34-0410-b5e6-96231b3b80d8