1  // { dg-do preprocess }
       2  // { dg-options "-std=gnu99 -fdiagnostics-show-option -Werror=undef" }
       3  /* { dg-message "some warnings being treated as errors" "" {target "*-*-*"} 0 } */
       4  #if x  // { dg-error "\"x\" is not defined, evaluates to 0 .-Werror=undef." }
       5  #endif