avformat/rtsp: #if unused functions away, fix -O0 compilation

parse_rtsp_message() is only called if the rtsp demuxer is enabled
and so it is normally compiled away if said demuxer is disabled.
Yet this does not happen when compiling with -O0 and this leads
to a linking failure because parse_rtsp_message() calls functions
that may not be available if the rtsp demuxer is disabled.
Fix this by properly #if'ing the unused functions away.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/rtsp.c

@@ -246,6 +246,7 @@ static void finalize_rtp_handler_init(AVFormatContext *s, RTSPStream *rtsp_st,
     }
 }
 
+#if CONFIG_RTSP_DEMUXER
 static int init_satip_stream(AVFormatContext *s)
 {
     RTSPState *rt = s->priv_data;
@@ -274,6 +275,7 @@ static int init_satip_stream(AVFormatContext *s)
     }
     return 0;
 }
+#endif
 
 /* parse the rtpmap description: <codec_name>/<clock_rate>[/<other params>] */
 static int sdp_parse_rtpmap(AVFormatContext *s,
@@ -2006,6 +2008,7 @@ redirect:
 #endif /* CONFIG_RTSP_DEMUXER || CONFIG_RTSP_MUXER */
 
 #if CONFIG_RTPDEC
+#if CONFIG_RTSP_DEMUXER
 static int parse_rtsp_message(AVFormatContext *s)
 {
     RTSPState *rt = s->priv_data;
@@ -2028,6 +2031,7 @@ static int parse_rtsp_message(AVFormatContext *s)
 
     return 0;
 }
+#endif
 
 static int udp_read_packet(AVFormatContext *s, RTSPStream **prtsp_st,
                            uint8_t *buf, int buf_size, int64_t wait_end)