This implements Jason's suggested approach: 'I'd think that the bug is
that we're treating them as types in the first place; they aren't
types, so they shouldn't reach comptypes.  I'd lean toward adding an
assert to that effect and fixing the caller to use
e.g. template_args_equal.'

	PR c++/93933
	* pt.c (template_args_equal): Pass ARGUMENT_PACKS through to
	cp_tree_equal.
	* tree.c (cp_tree_equal): Compare ARGUMENT_PACKS here,
	* typeck.c (comptypes): Assert we don't get any argument packs.