Allow use of argument param files for J2ObjC scripts.

--
MOS_MIGRATED_REVID=100964806

tools/j2objc/j2objc_wrapper.py

diff --git a/tools/j2objc/j2objc_wrapper.py b/tools/j2objc/j2objc_wrapper.py
index c3e5778..adae054 100755
--- a/tools/j2objc/j2objc_wrapper.py
+++ b/tools/j2objc/j2objc_wrapper.py
@@ -120,7 +120,7 @@
     input_file_queue.task_done()
 
 if __name__ == '__main__':
-  parser = argparse.ArgumentParser()
+  parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
   parser.add_argument(
       '--java',
       required=True,