Fix declarations of pthread functions, missed in recent commit.

src/port/pthread-win32.h

@@ -10,10 +10,10 @@ DWORD		pthread_self(void);
 void		pthread_setspecific(pthread_key_t, void *);
 void	   *pthread_getspecific(pthread_key_t);
 
-void		pthread_mutex_init(pthread_mutex_t *, void *attr);
-void		pthread_mutex_lock(pthread_mutex_t *);
+int			pthread_mutex_init(pthread_mutex_t *, void *attr);
+int			pthread_mutex_lock(pthread_mutex_t *);
 
 /* blocking */
-void		pthread_mutex_unlock(pthread_mutex_t *);
+int			pthread_mutex_unlock(pthread_mutex_t *);
 
 #endif