* decl.c (duplicate_decls): Copy DECL_TEMPLATE_INSTANTIATED when
	merging decls.
	* pt.c (regenerate_decl_from_template): Tweak for clarity.
	(instantiate_decl): Mark a decl instantiated before regenerating
	it to avoid recursion.
	* tree.c (mapcar): Don't call decl_constant_value unless we know
	something is TREE_READONLY_DECL_P.

From-SVN: r25458