C++: Remove FPs in cpp/wrong-type-format-argument caused by no linker awareness

cpp/ql/src/Likely Bugs/Format/WrongTypeFormatArguments.ql

@@ -171,7 +171,9 @@ where
   not arg.isAffectedByMacro() and
   not arg.isFromUninstantiatedTemplate(_) and
   not actual.stripType() instanceof ErroneousType and
-  not arg.(Call).mayBeFromImplicitlyDeclaredFunction()
+  not arg.(Call).mayBeFromImplicitlyDeclaredFunction() and
+  // Make sure that the format function definition is consistent
+  count(ffc.getTarget().getFormatParameterIndex()) = 1
 select arg,
   "This format specifier for type '" + expected.getName() + "' does not match the argument type '" +
     actual.getUnspecifiedType().getName() + "'."

cpp/ql/test/query-tests/Likely Bugs/Format/WrongTypeFormatArguments/Buildless/tests.c

@@ -10,3 +10,21 @@ void f(UNKNOWN_CHAR * str) {
     fprintf(0, "%s", ""); // GOOD
     printf("%s", str); // GOOD - erroneous type is ignored
 }
+
+#define va_list void*
+#define va_start(x, y) x = 0;
+#define va_arg(x, y) ((y)x)
+#define va_end(x)
+int vprintf(const char * format, va_list args);
+
+int my_printf(const char * format, ...) {
+    va_list args;
+    va_start(args, format);
+    int result = vprintf(format, args);
+    va_end(args);
+    return result;
+}
+
+void linker_awareness_test() {
+    my_printf("%s%d", "", 1);  // GOOD
+}

cpp/ql/test/query-tests/Likely Bugs/Format/WrongTypeFormatArguments/Buildless/tests2.c

@@ -0,0 +1,14 @@
+#define va_list void*
+#define va_start(x, y) x = 0;
+#define va_arg(x, y) ((y)x)
+#define va_end(x)
+
+int vprintf(const char * format, va_list args);
+
+int my_printf(void * p,const char * format, ...) {
+    va_list args;
+    va_start(args, format);
+    int result = vprintf(format, args);
+    va_end(args);
+    return result;
+}