if the merged definition is visible, and perform lookups into all merged copies
of the definition (not just for special members) so that we can complete the
redecl chains for members of the class.
llvm-svn: 233420
declaration of that entity in from one of those modules, keep track of the fact
that we've not completed the redeclaration chain yet so that we can pull the
remaining declarations in from the other module if they're needed.
llvm-svn: 209161