PR c++/48322
gcc/cp/
	* cp-tree.h (PACK_EXPANSION_EXTRA_ARGS): New.
	* cp-tree.def (EXPR_PACK_EXPANSION): Add an operand for it.
	* pt.c (tsubst_pack_expansion): Set and use it.
	(iterative_hash_template_arg): Hash it.
	(template_args_equal): Compare it.
	(comp_template_args_with_info): Handle nulls.
	* tree.c (cp_walk_subtrees): Walk it.
	* typeck.c (structural_comptypes): Compare it.
	* ptree.c (cxx_print_type): Print it.
libstdc++-v3/
	* include/std/tuple (tuple(_UElements&&...)): Fix SFINAE.

From-SVN: r181547