Refactor `mk_pat_db()` so that it is usable externally via a new function

``mk_pat_db_internal()`` which is called by a new ``mk_pat_db.py`` script. This
will allow other build systems to generate the ``database.h`` file.

scripts/mk_pat_db.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+"""
+Reads a pattern database and generates the corresponding
+header file.
+"""
+import mk_util
+import argparse
+import logging
+import os
+import sys
+
+def main(args):
+  logging.basicConfig(level=logging.INFO)
+  parser = argparse.ArgumentParser(description=__doc__)
+  parser.add_argument("db_file", help="pattern database file")
+  parser.add_argument("output_file", help="output header file path")
+  pargs = parser.parse_args(args)
+
+  if not os.path.exists(pargs.db_file):
+    logging.error('"{}" does not exist'.format(pargs.db_file))
+    return 1
+
+  if (os.path.exists(pargs.output_file) and
+     not os.path.isfile(pargs.output_file)):
+       logging.error('Refusing to overwrite "{}"'.format(
+         pargs.output_file))
+       return 1
+
+  mk_util.mk_pat_db_internal(pargs.db_file, pargs.output_file)
+  return 0
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))
+