lgtm: complain about ftok() use

Triggered by systemd#11555

.lgtm/cpp-queries/ftok.ql

@@ -0,0 +1,21 @@
+/**
+ * @name Use of ftok()
+ * @description ftok() is unsafe to call. Use extract_first_word() instead.
+ * @kind problem
+ * @problem.severity error
+ * @precision high
+ * @id cpp/ftok
+ * @tags reliability
+ *       security
+ */
+import cpp
+
+predicate dangerousFunction(Function function) {
+  exists (string name | name = function.getQualifiedName() |
+    name = "ftok")
+}
+
+from FunctionCall call, Function target
+where call.getTarget() = target
+  and dangerousFunction(target)
+select call, target.getQualifiedName() + " is potentially dangerous"