avcodec/libxvid_rc: Avoid strerror() for thread saftey

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libxvid_rc.c

@@ -69,7 +69,7 @@ av_cold int ff_xvid_rate_control_init(MpegEncContext *s)
 
         if (write(fd, tmp, strlen(tmp)) < 0) {
             int ret = AVERROR(errno);
-            av_log(NULL, AV_LOG_ERROR, "Error %s writing 2pass logfile\n", strerror(errno));
+            av_log(NULL, AV_LOG_ERROR, "Error %s writing 2pass logfile\n", av_err2str(ret));
             av_free(tmp_name);
             close(fd);
             return ret;