Add a missing dependency for the WebM muxer

This fixes one of the issues found if building with
--disable-everything --enable-muxer=webm

Originally committed as revision 26066 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/Makefile

@@ -286,7 +286,7 @@ OBJS-$(CONFIG_WAV_MUXER)                 += wav.o riff.o
 OBJS-$(CONFIG_WC3_DEMUXER)               += wc3movie.o
 OBJS-$(CONFIG_WEBM_MUXER)                += matroskaenc.o matroska.o \
                                             riff.o isom.o avc.o \
-                                            flacenc_header.o
+                                            flacenc_header.o avlanguage.o
 OBJS-$(CONFIG_WSAUD_DEMUXER)             += westwood.o
 OBJS-$(CONFIG_WSVQA_DEMUXER)             += westwood.o
 OBJS-$(CONFIG_WV_DEMUXER)                += wv.o apetag.o