PR c++/68422

	* cp-tree.h (PACK_EXPANSION_SIZEOF_P): New.
	* parser.c (cp_parser_sizeof_pack): Set it.
	* pt.c 	(tsubst_copy) [SIZEOF_EXPR]: Likewise.
	(tsubst_pack_expansion): Improve T... shortcut for expression packs.

From-SVN: r230629