Bug 1585751 - [lint.wpt] Work around mozprocess Windows + Python 3 bug, r=jgraham

Depends on D47975

Differential Revision: https://phabricator.services.mozilla.com/D47976

--HG--
extra : moz-landing-system : lando

tools/lint/wpt/wpt.py

@@ -39,6 +39,15 @@ def lint(files, config, **kwargs):
 
     proc = ProcessHandler(cmd, env=os.environ, processOutputLine=process_line,
                           universal_newlines=True)
+
+    if sys.platform == 'win32':
+        # Workaround for bug 1585702. According to the win32 docs,
+        # CreateProcess will use the calling process's env by default. Since we
+        # are passing in `os.environ` wholesale anyway, setting the env to
+        # `None` shouldn't make a difference. An alternative workaround would
+        # be to stop using mozprocess here and use subprocess directly.
+        proc.env = None
+
     proc.run()
     try:
         proc.wait()