bitbake: Add missing signature files

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/bin/bitbake-diffsigs

@@ -0,0 +1,9 @@
+#!/usr/bin/env python
+import os
+import sys
+import warnings
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(sys.argv[0])), 'lib'))
+
+import bb.siggen
+
+bb.siggen.compare_sigfiles(sys.argv[1], sys.argv[2])