c++: Fix qualified array-type construction [PR 98538]

This was an assert that was too picky.  The reason I had to alter
array construction was that on stream in, we cannot dynamically determine
a type's dependentness.  Thus on stream out of the 'problematic' types,
we save the dependentness for reconstruction.  Fortunately the paths into
cp_build_qualified_type_real from streamin with arrays do have the array's
dependentess set as needed.

	PR c++/98538
	gcc/cp/
	* tree.c (cp_build_qualified_type_real): Propagate an array's
	dependentness to the copy, if known.
	gcc/testsuite/
	* g++.dg/template/pr98538.C: New.

gcc/cp/tree.c

@@ -1340,10 +1340,12 @@ cp_build_qualified_type_real (tree type,
 
       if (!t)
 	{
-	  gcc_checking_assert (TYPE_DEPENDENT_P_VALID (type)
-			       || !dependent_type_p (type));
+	  /* If we already know the dependentness, tell the array type
+	     constructor.  This is important for module streaming, as we cannot
+	     dynamically determine that on read in.  */
 	  t = build_cplus_array_type (element_type, TYPE_DOMAIN (type),
-				      TYPE_DEPENDENT_P (type));
+				      TYPE_DEPENDENT_P_VALID (type)
+				      ? int (TYPE_DEPENDENT_P (type)) : -1);
 
 	  /* Keep the typedef name.  */
 	  if (TYPE_NAME (t) != TYPE_NAME (type))

gcc/testsuite/g++.dg/template/pr98538.C

@@ -0,0 +1,18 @@
+// PR c++/98538
+// { dg-do compile { target c++11 } }
+// ICE bulding a dependent array type variant
+
+template<typename T> using A = int[1];
+template<typename T, const A<T>> struct X { };
+
+template<typename T>
+void
+f (const A<T>)
+{
+  const A<T> a;
+}
+
+template<typename T>
+struct Y {
+  const A<T> a;
+};