[clang-format] Add return code to git-clang-format

[owenpan]

Summary

Fixes https://github.com/llvm/llvm-project/issues/53220.

[curdeius]

LGTM!

[MyDeveloperDay]

So simple but so nice, LGTM

clang/tools/clang-format/git-clang-format

if ignored_files:
       print(
         'Ignoring changes in the following files (wrong extension or symlink):')
       for filename in ignored_files:
         print('    %s' % filename)
     if changed_lines:
       print('Running clang-format on the following files:')
       for filename in changed_lines:
         print('    %s' % filename)
+
   if not changed_lines:
     if opts.verbose >= 0:
       print('no modified files to format')
-    return
+    return 0
+
   if len(commits) > 1:
     old_tree = commits[1]
     new_tree = run_clang_format_and_save_to_tree(changed_lines,
                                                  revision=commits[1],
                                                  binary=opts.binary,
                                                  style=opts.style)
   else:
     old_tree = create_tree_from_workdir(changed_lines)
     new_tree = run_clang_format_and_save_to_tree(changed_lines,
                                                  binary=opts.binary,
                                                  style=opts.style)
   if opts.verbose >= 1:
     print('old tree: %s' % old_tree)
     print('new tree: %s' % new_tree)
+
   if old_tree == new_tree:
     if opts.verbose >= 0:
       print('clang-format did not modify any files')
-  elif opts.diff:
+    return 0
+
+  if opts.diff:
     print_diff(old_tree, new_tree)
   elif opts.diffstat:
     print_diffstat(old_tree, new_tree)
   else:
     changed_files = apply_changes(old_tree, new_tree, force=opts.force,
                                   patch_mode=opts.patch)
     if (opts.verbose >= 0 and not opts.patch) or opts.verbose >= 1:
       print('changed files:')
       for filename in changed_files:
         print('    %s' % filename)
 
+  return 1
+
 
 def load_git_config(non_string_options=None):
   """Return the git configuration as a dictionary.
 
   All options are assumed to be strings unless in `non_string_options`, in which
   is a dictionary mapping option name (in lower case) to either "--bool" or
   "--int"."""
   if non_string_options is None: