Extend using-for.

test/libsolidity/semanticTests/using/free_functions_individual.sol

@@ -0,0 +1,30 @@
+using {zero} for uint;
+
+contract C {
+    using {id} for uint;
+
+    function f(uint z) pure external returns(uint) {
+        return z.id();
+    }
+
+    function g(uint z) pure external returns (uint) {
+        return z.zero();
+    }
+}
+
+function id(uint x) pure returns (uint) {
+    return x;
+}
+
+function zero(uint) pure returns (uint) {
+    return 0;
+}
+
+
+// ====
+// compileViaYul: also
+// ----
+// f(uint256): 10 -> 10
+// g(uint256): 10 -> 0
+// f(uint256): 256 -> 0x0100
+// g(uint256): 256 -> 0