pthread_t定义结构

linux下被定义为：

在linux履行pthread_t它被定义为 "unsigned long int",参考这里

Windows下这样定义：

    /*
     * Generic handle type - intended to extend uniqueness beyond
     * that available with a simple pointer. It should scale for either
     * IA-32 or IA-64.
     */
    typedef struct {
        void * p;                   /* Pointer to actual object */
        unsigned int x;             /* Extra information - reuse count etc */
    } ptw32_handle_t;
    typedef ptw32_handle_t pthread_t;