config-dos.h: define HAVE_TERMIOS_H only for djgpp

#define HAVE_SYS_SOCKET_H      1

#define HAVE_SYS_STAT_H        1

#define HAVE_SYS_TYPES_H       1

#define HAVE_TERMIOS_H         1

#define HAVE_TIME_H            1

#define HAVE_UNISTD_H          1

  #define HAVE_SIGACTION  1

  #define HAVE_SIGSETJMP  1

  #define HAVE_SYS_TIME_H 1

  #define HAVE_TERMIOS_H  1

  #define HAVE_VARIADIC_MACROS_GCC 1

  /* Because djgpp <= 2.03 doesn't have snprintf() etc. */