bpo-20891: Py_Initialize() now creates the GIL (#4700)

The GIL is no longer created "on demand" to fix a race condition when
PyGILState_Ensure() is called in a non-Python thread.

Python/pylifecycle.c

@@ -681,9 +681,13 @@ _Py_InitializeCore(const _PyCoreConfig *core_config)
        Instead we destroy the previously created GIL here, which ensures
        that we can call Py_Initialize / Py_FinalizeEx multiple times. */
     _PyEval_FiniThreads();
+
     /* Auto-thread-state API */
     _PyGILState_Init(interp, tstate);
 
+    /* Create the GIL */
+    PyEval_InitThreads();
+
     _Py_ReadyTypes();
 
     if (!_PyFrame_Init())