av_rpi_zc_get_buffer2 is declared but it has no implementation #1

I managed to use hevc hardware support via rpi_zc in my application by adding the following to my get_format2:

        if (inFmt[i] == AV_PIX_FMT_RPI4_8) {
            bcm_host_init();
            vcsm_init_ex (1, -1);
            ZcEnv *theEnv = av_rpi_zc_int_env_alloc (inContext);
            av_rpi_zc_init2 (inContext, theEnv->pool_env, theEnv->alloc_buf, theEnv->free_pool);
            inContext->refcounted_frames = 1;
            av_free (theEnv);
            return inFmt[i];
        }

In addition I had to copy the declarations of struct AVZcEnv and struct ZcOldCtxVals from rpi_zc.c. av_rpi_zc_get_buffer2 is declared in rpi_zc.h, but it has no implementation. The implementation is called zc_get_buffer2 in rpi_zc.c, but it is not exported. So my hack seems the only way to use rpi_zc. In a previous version of the hevc patch, av_rpi_zc_init that required no parameters, was available.