* s/dgux.h: Changes from Paul M Reilly <pmr@rock.concert.net>:
(BSD4_4, SVR4, HAVE_SETSID, HAVE_UNIX_DOMAIN): #define these.
(FIRST_PTY_LETTER): This is 'r', not 'p'.
(HAVE_TERMIO, SIGNALS_VIA_CHARACTERS): Don't #define these.
(HAVE_TERMIOS): #define these instead.
(XREBINDKEYSYM): Don't #define.
Test THIS_IS_YMAKEFILE instead of MAKING_MAKEFILE.
(sigmask, sigpause): #undef these after #including <signal.h>.
(LD_SWITCH_SYSTEM, START_FILES, LIBS_SYSTEM, LIB_GCC): #define
these to avoid problems with /lib/crt0.o.
(C_DEBUG_SWITCH, C_OPTIMIZE_SWITCH): #define these.