c++: ICE with unexpanded pack in do-while [PR99063]

c++: ICE with unexpanded pack in do-while [PR99063]

Here an unexpanded parameter pack snuck into prep_operand which doesn't
expect to see an operand without a type, and since r247842
NONTYPE_ARGUMENT_PACK doesn't have a type anymore.

This only happens with the do-while loop whose condition may not
contain a declaration so we never called finish_cond which checks
for unexpanded parameter packs.  So use check_for_bare_parameter_packs
to remedy that.

gcc/cp/ChangeLog:

	PR c++/99063
	* semantics.c (finish_do_stmt): Check for unexpanded parameter packs.

gcc/testsuite/ChangeLog:

	PR c++/99063
	* g++.dg/cpp0x/variadic-crash6.C: New test.