Add PyInterpreterState.override_multi_interp_extensions_check.

Author: ericsnowcurrently

Include/internal/pycore_interp.h

@@ -123,6 +123,7 @@ struct _is {
     // override for config->use_frozen_modules (for tests)
     // (-1: "off", 1: "on", 0: no override)
     int override_frozen_modules;
+    int override_multi_interp_extensions_check;
 
     PyObject *codec_search_path;
     PyObject *codec_search_cache;

Python/import.c

@@ -2400,7 +2400,9 @@ _PyImport_CheckSubinterpIncompatibleExtensionAllowed(const char *name)
 {
     PyInterpreterState *interp = _PyInterpreterState_Get();
     if (_PyInterpreterState_HasFeature(
-                interp, Py_RTFLAGS_MULTI_INTERP_EXTENSIONS)) {
+                interp, Py_RTFLAGS_MULTI_INTERP_EXTENSIONS) &&
+        !interp->override_multi_interp_extensions_check
+    ) {
         assert(!_Py_IsMainInterpreter(interp));
         PyErr_Format(PyExc_ImportError,
                      "module %s does not support loading in subinterpreters",