1  // { dg-do preprocess }
       2  // { dg-options "-std=gnu99 -fdiagnostics-show-option -trigraphs -Werror=trigraphs" }
       3  /* { dg-message "some warnings being treated as errors" "" {target "*-*-*"} 0 } */
       4  ??=  // { dg-error "trigraph \\?\\?= converted to # .-Werror=trigraphs." }