The c93 demuxer depends on vocdec.o.

This fixes the following option set:
  --disable-encoders --disable-decoders --disable-parsers --disable-bsfs
  --disable-muxers --disable-demuxers --disable-protocols --enable-demuxer=c93

Originally committed as revision 9642 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/Makefile

@@ -32,7 +32,7 @@ OBJS-$(CONFIG_AVI_MUXER)                 += avienc.o riff.o
 OBJS-$(CONFIG_AVISYNTH)                  += avisynth.o
 OBJS-$(CONFIG_AVS_DEMUXER)               += avs.o vocdec.o voc.o riff.o
 OBJS-$(CONFIG_BETHSOFTVID_DEMUXER)       += bethsoftvid.o
-OBJS-$(CONFIG_C93_DEMUXER)               += c93.o
+OBJS-$(CONFIG_C93_DEMUXER)               += c93.o vocdec.o voc.o
 OBJS-$(CONFIG_CRC_MUXER)                 += crc.o
 OBJS-$(CONFIG_DAUD_DEMUXER)              += daud.o
 OBJS-$(CONFIG_DC1394_DEMUXER)            += dc1394.o