make: unifdef SUN5_0 (defined)

*** 10,19 ****
  #
  
  # Copyright 2015, Richard Lowe.
  
  MAKE_INCLUDE= $(SRC)/cmd/make/include
! MAKE_DEFS= -DSUN5_0 -DSYSV -DINTER -DSUNOS4_AND_AFTER
  $(RELEASE_BUILD)MAKE_DEFS += -DNDEBUG
  CFLAGS += $(CCVERBOSE)
  CPPFLAGS += -I$(MAKE_INCLUDE) $(MAKE_DEFS)
  
--- 10,19 ----
  #
  
  # Copyright 2015, Richard Lowe.
  
  MAKE_INCLUDE= $(SRC)/cmd/make/include
! MAKE_DEFS= -DSYSV -DINTER -DSUNOS4_AND_AFTER
  $(RELEASE_BUILD)MAKE_DEFS += -DNDEBUG
  CFLAGS += $(CCVERBOSE)
  CPPFLAGS += -I$(MAKE_INCLUDE) $(MAKE_DEFS)