make: unifdef SUN5_0 (defined)

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