LL库 printf重定向

#ifdef __GNUC__
    #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
    #define PUTCHAR_PROTOTYPE int fputc(int ch,FILE *f)
#endif
PUTCHAR_PROTOTYPE {
    LL_USART_TransmitData8(USART1,(uint8_t)ch);
    while(!LL_USART_IsActiveFlag_TXE(USART1));
    return ch;
}