deps: backport 9c927d0f01 from V8 upstream

Original commit message:

    [test] Set default locale in test runner

    BUG=v8:4437,v8:2899,chromium:604310
    LOG=n

    Review URL: https://codereview.chromium.org/1402373002

    Cr-Commit-Position: refs/heads/master@{#35614}

PR-URL: https://github.com/nodejs/node/pull/7451
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

deps/v8/tools/run-tests.py

@@ -326,6 +326,9 @@ def ProcessOptions(options):
   global VARIANT_FLAGS
   global VARIANTS
 
+  # Many tests assume an English interface.
+  os.environ['LANG'] = 'en_US.UTF-8'
+
   # Architecture and mode related stuff.
   if options.arch_and_mode:
     options.arch_and_mode = [arch_and_mode.split(".")