Export _Py_yield.

Author: ZeroIntensity

Include/internal/pycore_lock.h

@@ -71,7 +71,8 @@ PyMutex_LockFlags(PyMutex *m, _PyLockFlags flags)
 extern int _PyMutex_TryUnlock(PyMutex *m);
 
 // Yield the processor to other threads (e.g., sched_yield).
-extern void _Py_yield(void);
+// Exported for _testembed.
+PyAPI_FUNC(void) _Py_yield(void);
 
 
 // PyEvent is a one-time event notification