[PR94044] Fix ICE with sizeof<argumentpack>

Thanks to Jim for figuring out how to reproduce the problem, I was
able to apply pr94044-jig.diff to poorly hash the specialization
table. (That places all the specializations of a particular template
in the same bucket, forcing us to compare the arguments.)

The testcase creates sizeof_exprs containing argument packs, and we
can no longer use same_type_p on those.

	PR c++/94044
	* tree.c (cp_tree_equal) [SIZEOF_EXPR]: Detect argument pack
	operand.

gcc/cp/ChangeLog

+2020-03-23  nathans  <nathan@acm.org>
+
+	PR c++/94044
+	* tree.c (cp_tree_equal) [SIZEOF_EXPR]: Detect argument pack
+	operand.
+
 2020-03-21  Patrick Palka  <ppalka@redhat.com>
 
 	PR c++/94066

gcc/cp/tree.c

@@ -3802,9 +3802,13 @@ cp_tree_equal (tree t1, tree t2)
 	    if (SIZEOF_EXPR_TYPE_P (t2))
 	      o2 = TREE_TYPE (o2);
 	  }
+
 	if (TREE_CODE (o1) != TREE_CODE (o2))
 	  return false;
-	if (TYPE_P (o1))
+
+	if (ARGUMENT_PACK_P (o1))
+	  return template_args_equal (o1, o2);
+	else if (TYPE_P (o1))
 	  return same_type_p (o1, o2);
 	else
 	  return cp_tree_equal (o1, o2);