doc: clarify -Werror * doc/warnings.texi (warnings): -Werror is not always a bad idea; clarify that it's intended for developers, not for ordinary builds, and mention --enable-gcc-warnings as one possible use.

#ifndef DEV_INO_H
# define DEV_INO_H 1

# include <sys/types.h>
# include <sys/stat.h>

struct dev_ino
{
  ino_t st_ino;
  dev_t st_dev;
};

#endif