use $^ instead of $? for the prereqs for the ans2asc link command

Fixes the link failure when sauce.o didn't need to be rebuilt.

src/sbbs3/GNUmakefile

@@ -218,7 +218,7 @@ $(JSEXEC): $(JSEXEC_OBJS) $(SBBS)
 # ANS2ASC
 $(ANS2ASC): $(OBJODIR)/ans2asc.o $(OBJODIR)/sauce.o $(XPDEV_LIB)
 	@echo Linking $@
-	$(QUIET)$(CC) $(CONSOLE_LDFLAGS) -o $@ $? -lm
+	$(QUIET)$(CC) $(CONSOLE_LDFLAGS) -o $@ $^ -lm
 
 # ASC2ANS
 $(ASC2ANS): $(OBJODIR)/asc2ans.o