Allow selecting only the vc1 demuxer.

This fixes the following option set:
  --disable-encoders --disable-decoders --disable-parsers --disable-bsfs
  --disable-muxers --disable-demuxers --disable-protocols
  --enable-demuxer=vc1

Originally committed as revision 9649 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/Makefile

@@ -135,6 +135,7 @@ OBJS-$(CONFIG_TIERTEXSEQ_DEMUXER)        += tiertexseq.o
 OBJS-$(CONFIG_TTA_DEMUXER)               += tta.o
 OBJS-$(CONFIG_TXD_DEMUXER)               += txd.o
 OBJS-$(CONFIG_V4L2_DEMUXER)              += v4l2.o
+OBJS-$(CONFIG_VC1_DEMUXER)               += raw.o
 OBJS-$(CONFIG_VIDEO_GRAB_BKTR_DEMUXER)   += grab_bktr.o
 OBJS-$(CONFIG_VIDEO_GRAB_V4L_DEMUXER)    += grab.o
 OBJS-$(CONFIG_VMD_DEMUXER)               += sierravmd.o