PR c++/80891 (#1,#5)
	* cp-tree.h (lookup_maybe_add): Add DEDUPING argument.
	* name-lookup.c (name_lookup): Add deduping field.
	(name_lookup::preserve_state, name_lookup::restore_state): Deal
	with deduping.
	(name_lookup::add_overload): New.
	(name_lookup::add_value, name_lookup::add_fns): Call add_overload.
	(name_lookup::search_adl): Set deduping.  Don't unmark here.
	* pt.c (most_specialized_instantiation): Revert previous change,
	Assert not given duplicates.
	* tree.c (lookup_mark): Just mark the underlying decls.
	(lookup_maybe_add): Dedup using marked decls.

	PR c++/80891 (#5)
	* g++.dg/lookup/pr80891-5.C: New.

From-SVN: r248578