MT#55283 add lib/ Makefile

There is a generated file left behind (codeclib.strhash.c) that needs to
be cleaned up by `make clean`

Ref: https://bugs.debian.org/1101804
Change-Id: I22eef1124a84107478ef6058abb127eb65fc9aa5

Makefile

@@ -67,6 +67,7 @@ distclean clean:
 	$(MAKE) -C perf-tester clean
 	$(MAKE) -C kernel-module clean
 	$(MAKE) -C t clean
+	$(MAKE) -C lib clean
 	rm -f config.mk
 
 .DEFAULT:

lib/Makefile

@@ -0,0 +1,7 @@
+.PHONY: clean distclean
+
+.DEFAULT:
+	true
+
+clean distclean:
+	rm -f *.strhash.*