add clean and coverity targets for make

Makefile

@@ -1,13 +1,24 @@
 SUBDIRS = src docs
+CLEANDIRS = $(SUBDIRS:%=clean-%)
 
 .PHONY: all $(SUBDIRS)
 
 all: $(SUBDIRS)
 
 $(SUBDIRS): %:
-	echo "Making $@"
+	@echo "Making $@"
 	@$(MAKE) -C $@
 
 update-fossa:
 	git subtree pull --prefix deps/fossa https://github.com/cesanta/fossa master --squash
 
+# Remember to add the coverity bin directory to your PATH
+coverity-build: $(CLEANDIRS)
+	cov-build --dir cov-int make src
+	@tar caf jittertrap-coverity-build.lzma cov-int
+	@echo Coverity build archive: jittertrap-coverity-build.lzma
+
+clean: $(CLEANDIRS)
+$(CLEANDIRS):
+	@echo "Cleaning $@"
+	$(MAKE) -C $(@:clean-%=%) clean

docs/Makefile

@@ -2,3 +2,6 @@
 # Do nothing, for now.
 
 all:
+
+clean:
+