Bug 844509 - Always encode config.status as utf-8. r=nalexander

Now that there is no bytes strings in it, we don't need to store
config.status in the system encoding to keep those valid. Moreover, the
system encoding is lossy, which utf-8 is not.

Differential Revision: https://phabricator.services.mozilla.com/D42731

configure.py

@@ -24,7 +24,6 @@ from mozbuild.pythonutil import iter_modules_in_path
 from mozbuild.backend.configenvironment import PartialConfigEnvironment
 from mozbuild.util import (
     indented_repr,
-    system_encoding,
 )
 import mozpack.path as mozpath
 import six
@@ -102,12 +101,12 @@ def config_status(config):
     # here, when we're able to skip configure tests/use cached results/not rely
     # on autoconf.
     logging.getLogger('moz.configure').info('Creating config.status')
-    with codecs.open('config.status', 'w', system_encoding) as fh:
+    with codecs.open('config.status', 'w', 'utf-8') as fh:
         fh.write(textwrap.dedent('''\
             #!%(python)s
-            # coding=%(encoding)s
+            # coding=utf-8
             from __future__ import unicode_literals
-        ''') % {'python': config['PYTHON'], 'encoding': system_encoding})
+        ''') % {'python': config['PYTHON']})
         for k, v in six.iteritems(sanitized_config):
             fh.write('%s = %s\n' % (k, indented_repr(v)))
         fh.write("__all__ = ['topobjdir', 'topsrcdir', 'defines', "