gcc/gcc/testsuite/gcc.dg/cpp/cmdlne-dU-17.c

/* { dg-do preprocess } */
/* { dg-options "-P -dU" } */
/* { dg-final { scan-file cmdlne-dU-17.i "^\n*1\n+#define __STDC__ 1\n*$" } } */
__STDC__