Bug 1423809 - Support localized generated files in the tup backend; r=nalexander

These files fail to build in the tup backend because the --locale
argument is missing and scripts like generate_update_locale.py require a
locale. Since the tup backend currently only supports en-US, we can just
hardcode this argument for now.

MozReview-Commit-ID: 7Js1yd9QB01

--HG--
extra : rebase_source : 387b5cfd0379ae3fd857e8c58722cfbca189e058

python/mozbuild/mozbuild/backend/tup.py

@@ -331,6 +331,8 @@ class TupOnly(CommonBackend, PartialBackend):
         if obj.script and obj.method and obj.relobjdir not in skip_directories:
             backend_file.export_shell()
             cmd = self._py_action('file_generate')
+            if obj.localized:
+                cmd.append('--locale=en-US')
             cmd.extend([
                 obj.script,
                 obj.method,