BUILD: makefile: mark poll and tcploop targets as phony

Since these ones come with their own makefiles, the top-level makefile
cannot decide when they have to be rebuilt, it should always defer the
decision to the compoent's makefile, so we must mark them as phony.
Because of these, they were not updated after a change without calling
a "clean" first.
diff --git a/Makefile b/Makefile
index 8e70ab7..3e765ae 100644
--- a/Makefile
+++ b/Makefile
@@ -1043,7 +1043,7 @@
 	$(cmd_LD) $(LDFLAGS) -o $@ $^ $(LDOPTS)
 
 # rebuild it every time
-.PHONY: src/version.c
+.PHONY: src/version.c dev/poll/poll dev/tcploop/tcploop
 
 src/calltrace.o: src/calltrace.c $(DEP)
 	$(cmd_CC) $(TRACE_COPTS) -c -o $@ $<