+COMMIT_HASH_FILE = confhash.h
+COMMIT_HASH_NONE = "[changed files]"
+
+# get last Git commit hash, if no files were changed
+SOURCE_HASH_STRING ?= $(shell test -d ../.git && test `git ls-files -m | wc -l` -eq 0 && git show -s --format=%h || echo "$(COMMIT_HASH_NONE)")
+