don't try to format includes on windows

It's not going to work:
   - windows\style\paths don't work well in Python
   - something seems to be slipping in extra \r, probably print?

Change-Id: I6d9a0cc0bff403b9b45412b0e92290a9346bcf14
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/230641
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

PRESUBMIT.py

@@ -198,7 +198,8 @@ def _CheckIncludesFormatted(input_api, output_api):
   cmd = ['python',
          'tools/rewrite_includes.py',
          '--dry-run'] + files
-  if 0 != subprocess.call(cmd):
+  # TODO(mtklein): tools/rewrite_includes.py doesn't work on Windows.
+  if 'win32' not in sys.platform and 0 != subprocess.call(cmd):
     return [output_api.PresubmitError('`%s` failed' % ' '.join(cmd))]
   return []