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/Tools/scripts/run_tests.py b/Tools/scripts/run_tests.py
index f750e19..e2a2050 100755
--- a/Tools/scripts/run_tests.py
+++ b/Tools/scripts/run_tests.py
@@ -10,6 +10,10 @@
 import os
 import sys
 import test.support
+try:
+    import threading
+except ImportError:
+    threading = None
 
 
 def is_multiprocess_flag(arg):
@@ -34,7 +38,7 @@
                  ])
     if sys.platform == 'win32':
         args.append('-n')         # Silence alerts under Windows
-    if not any(is_multiprocess_flag(arg) for arg in regrtest_args):
+    if threading and not any(is_multiprocess_flag(arg) for arg in regrtest_args):
         args.extend(['-j', '0'])  # Use all CPU cores
     if not any(is_resource_use_flag(arg) for arg in regrtest_args):
         args.extend(['-u', 'all,-largefile,-audio,-gui'])