Add help target to list available targets

build/make.help

@@ -0,0 +1,7 @@
+define print_help
+@make -pqR : 2>/dev/null \
+        | awk -v RS= -F: '/^# File/,/^# Finished Make data base/ {if ($$1 !~ "^[#.]") {print $$1}}' \
+        | sort \
+        | grep -E -v -e '^[^[:alnum:]]' -e '^$@$$' \
+				| xargs -I _ echo _
+endef