Fix compilation of _testembed.c without threads

Modules/_testembed.c

@@ -17,7 +17,9 @@ void print_subinterp(void)
 int main(int argc, char *argv[])
 {
     PyThreadState *mainstate, *substate;
+#ifdef WITH_THREAD
     PyGILState_STATE gilstate;
+#endif
     int i, j;
 
     for (i=0; i<3; i++) {
@@ -28,10 +30,12 @@ int main(int argc, char *argv[])
         Py_Initialize();
         mainstate = PyThreadState_Get();
 
+#ifdef WITH_THREAD
         PyEval_InitThreads();
         PyEval_ReleaseThread(mainstate);
 
         gilstate = PyGILState_Ensure();
+#endif
         print_subinterp();
         PyThreadState_Swap(NULL);
 
@@ -43,7 +47,9 @@ int main(int argc, char *argv[])
 
         PyThreadState_Swap(mainstate);
         print_subinterp();
+#ifdef WITH_THREAD
         PyGILState_Release(gilstate);
+#endif
 
         PyEval_RestoreThread(mainstate);
         Py_Finalize();