compilation warning "jobserver unavailable" removal

This commit removes the warning:
make[4]: warning: jobserver unavailable: using -j1.  Add '+' to parent make rule.

Basically, inside a Makefile we should use $(MAKE) instead of make.

common/utils/T/Makefile

@@ -27,4 +27,4 @@ check_vcd:
 
 clean:
 	rm -f *.o $(GENIDS) core T_IDs.h T_messages.txt.h _check_vcd
-	cd tracer && make clean
+	cd tracer && $(MAKE) clean

common/utils/T/tracer/Makefile

@@ -63,16 +63,16 @@ multi: multi.o utils.o database.o config.o
 .PHONY: all gui/gui.a view/view.a logger/logger.a filter/filter.a
 
 gui/gui.a:
-	cd gui && make
+	cd gui && $(MAKE)
 
 view/view.a:
-	cd view && make
+	cd view && $(MAKE)
 
 logger/logger.a:
-	cd logger && make
+	cd logger && $(MAKE)
 
 filter/filter.a:
-	cd filter && make
+	cd filter && $(MAKE)
 
 %.o: %.c
 	$(CC) $(CFLAGS) -c -o $@ $<
@@ -81,8 +81,8 @@ clean:
 	rm -f *.o core tracer_remote textlog enb ue vcd record replay
 	rm -f extract_config macpdu2wireshark extract_input_subframe
 	rm -f extract_output_subframe to_vcd extract multi
-	cd gui && make clean
-	cd view && make clean
-	cd logger && make clean
-	cd filter && make clean
-	cd hacks && make clean
+	cd gui && $(MAKE) clean
+	cd view && $(MAKE) clean
+	cd logger && $(MAKE) clean
+	cd filter && $(MAKE) clean
+	cd hacks && $(MAKE) clean