Move private function _args_from_interpreter_flags() to subprocess.py, so
that it can be imported when threads are disabled.
(followup to issue #12098)
diff --git a/Lib/test/support.py b/Lib/test/support.py
index 5259e27..e43dbad 100644
--- a/Lib/test/support.py
+++ b/Lib/test/support.py
@@ -1596,8 +1596,7 @@
 def args_from_interpreter_flags():
     """Return a list of command-line arguments reproducing the current
     settings in sys.flags and sys.warnoptions."""
-    from multiprocessing.util import _args_from_interpreter_flags
-    return _args_from_interpreter_flags()
+    return subprocess._args_from_interpreter_flags()
 
 #============================================================
 # Support for assertions about logging.