c++: sizeof... mangling with alias template [PR95298]

c++: sizeof... mangling with alias template [PR95298]

We were getting sizeof... mangling wrong when the argument after
substitution was a pack expansion that is not a simple T..., such as
list<T>... in variadic-mangle4.C or (A+1)... in variadic-mangle5.C.  In the
former case we ICEd; in the latter case we wrongly mangled it as sZ
<expression>.

	PR c++/95298

gcc/cp/ChangeLog:

	* mangle.cc (write_expression): Handle v18 sizeof... bug.
	* pt.cc (tsubst_pack_expansion): Keep TREE_VEC for sizeof...
	(tsubst_expr): Don't strip TREE_VEC here.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/variadic-mangle2.C: Add non-member.
	* g++.dg/cpp0x/variadic-mangle4.C: New test.
	* g++.dg/cpp0x/variadic-mangle5.C: New test.
	* g++.dg/cpp0x/variadic-mangle5a.C: New test.