Extend using-for.

test/libsolidity/syntaxTests/using/library_non_free_function.sol

@@ -0,0 +1,13 @@
+library L {
+    function id(uint x) internal pure returns(uint) {
+        return x;
+    }
+}
+
+contract C {
+    using {L.id} for uint;
+    function f(uint x) external pure {
+        x.id();
+    }
+}
+// ----