better way to test/set cygwin proc setting

xonsh/environ.py

@@ -1304,7 +1304,7 @@ def DEFAULT_VARS():
             is_bool_or_none,
             to_bool_or_none,
             bool_or_none_to_str,
-            True,
+            True if not ON_CYGWIN else False,
             "Whether or not to try to run subrocess mode in a Python thread, "
             "when applicable. There are various trade-offs, which normally "
             "affects only interactive sessions.\n\nWhen True:\n\n"

xonsh/proc.py

@@ -2033,8 +2033,7 @@ class CommandPipeline:
         # read from process now that it is over
         yield from safe_readlines(stdout)
         self.stream_stderr(safe_readlines(stderr))
-        if not ON_CYGWIN:
-            proc.wait()
+        proc.wait()
         self._endtime()
         yield from safe_readlines(stdout)
         self.stream_stderr(safe_readlines(stderr))