[clang-tidy] Add export-fixes flag to clang-tidy-diff

[juliehockett]

Summary

So that you can export the fixes generated.

[hokein]

looks good.

clang-tools-extra/trunk/clang-tidy/tool/clang-tidy-diff.py

def main():
   parser.add_argument('-fix', action='store_true', default=False,
                       help='apply suggested fixes')
   parser.add_argument('-checks',
                       help='checks filter, when not specified, use clang-tidy '
                       'default',
                       default='')
   parser.add_argument('-path', dest='build_path',
                       help='Path used to read a compile command database.')
+  parser.add_argument('-export-fixes', metavar='FILE', dest='export_fixes',
+                      help='Create a yaml file to store suggested fixes in, '
+                      'which can be applied with clang-apply-replacements.')
   parser.add_argument('-extra-arg', dest='extra_arg',
                       action='append', default=[],
                       help='Additional argument to append to the compiler '
                       'command line.')
   parser.add_argument('-extra-arg-before', dest='extra_arg_before',
                       action='append', default=[],
                       help='Additional argument to prepend to the compiler '
                       'command line.')
def main():
   else:
     quote = "'";
 
   # Run clang-tidy on files containing changes.
   command = [args.clang_tidy_binary]
   command.append('-line-filter=' + quote + line_filter_json + quote)
   if args.fix:
     command.append('-fix')
+  if args.export_fixes:
+    command.append('-export-fixes=' + args.export_fixes)
   if args.checks != '':
     command.append('-checks=' + quote + args.checks + quote)
   if args.quiet:
     command.append('-quiet')
   if args.build_path is not None:
     command.append('-p=%s' % args.build_path)
   command.extend(lines_by_file.keys())
   for arg in args.extra_arg: