C++: Add strcpy test for cpp/non-constant-format

Author: jketema

cpp/ql/test/query-tests/Likely Bugs/Format/NonConstantFormat/NonConstantFormat.expected

@@ -19,3 +19,4 @@
 | test.cpp:93:12:93:18 | ++ ... | The format string argument to printf should be constant to prevent security issues and other potential errors. |
 | test.cpp:110:12:110:24 | new[] | The format string argument to printf should be constant to prevent security issues and other potential errors. |
 | test.cpp:130:20:130:26 | access to array | The format string argument to sprintf should be constant to prevent security issues and other potential errors. |
+| test.cpp:157:12:157:15 | data | The format string argument to printf should be constant to prevent security issues and other potential errors. |

cpp/ql/test/query-tests/Likely Bugs/Format/NonConstantFormat/test.cpp

@@ -151,3 +151,8 @@ void print_ith_message() {
   set_value_of(&i);
   printf(messages[i], 1U); // GOOD
 }
+
+void fmt_via_strcpy(char *data) {
+    strcpy(data, "some string");
+    printf(data);
+}