re PR c++/68965 (`-Wunused-parameter` is reported in variadic lambda or function using sizeof...(xs))

	PR c++/68965
	* pt.c (tsubst_copy): Mark elements in expanded vector as used.

	* g++.dg/cpp1y/parameter-pack-1.C: New test.
	* g++.dg/cpp1y/parameter-pack-2.C: New test.

From-SVN: r232569