Teach the AST dumper to dump the canonical declaration for a mergeable declaration.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192739 91177308-0d34-0410-b5e6-96231b3b80d8
C++ modules: merging for enumerations and enumerators with multiple definitions
(eg through template instantiations in multiple modules).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192740 91177308-0d34-0410-b5e6-96231b3b80d8