trace: remove timestamp files when cleaning up

'make clean' did not remove trace.[ch]-timestamp files,
only trace.[ch]. But 'make' did not know how to make trace.[ch]
files if the timestamp files were present.

Fix by removing the timestamp files along with trace.[ch].

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

Makefile

@@ -153,7 +153,7 @@ clean:
 	rm -f *.o *.d *.a $(TOOLS) TAGS cscope.* *.pod *~ */*~
 	rm -f slirp/*.o slirp/*.d audio/*.o audio/*.d block/*.o block/*.d net/*.o net/*.d fsdev/*.o fsdev/*.d ui/*.o ui/*.d
 	rm -f qemu-img-cmds.h
-	rm -f trace.c trace.h
+	rm -f trace.c trace.h trace.c-timestamp trace.h-timestamp
 	$(MAKE) -C tests clean
 	for d in $(ALL_SUBDIRS) libhw32 libhw64 libuser libdis libdis-user; do \
 	if test -d $$d; then $(MAKE) -C $$d $@ || exit 1; fi; \