make swresample optional for ffmpeg

Signed-off-by: Paul B Mahol <onemda@gmail.com>

configure

@@ -3459,7 +3459,7 @@ avfilter_extralibs="pthreads_extralibs"
 avutil_extralibs="d3d11va_extralibs nanosleep_extralibs pthreads_extralibs vaapi_drm_extralibs vaapi_x11_extralibs vdpau_x11_extralibs"
 
 # programs
-ffmpeg_deps="avcodec avfilter avformat swresample"
+ffmpeg_deps="avcodec avfilter avformat"
 ffmpeg_select="aformat_filter anull_filter atrim_filter format_filter
                null_filter
                trim_filter"

fftools/ffmpeg_opt.c

@@ -3157,7 +3157,9 @@ void show_help_default(const char *opt, const char *arg)
 #if CONFIG_SWSCALE
         show_help_children(sws_get_class(), flags);
 #endif
+#if CONFIG_SWRESAMPLE
         show_help_children(swr_get_class(), AV_OPT_FLAG_AUDIO_PARAM);
+#endif
         show_help_children(avfilter_get_class(), AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM);
         show_help_children(av_bsf_get_class(), AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_BSF_PARAM);
     }