Fix compilation with --disable-everything --enable-muxer=avi --disable-network.

Fixes ticket #3568.

libavformat/Makefile

@@ -84,7 +84,7 @@ OBJS-$(CONFIG_AST_MUXER)                 += ast.o astenc.o
 OBJS-$(CONFIG_AU_DEMUXER)                += au.o pcm.o
 OBJS-$(CONFIG_AU_MUXER)                  += au.o rawenc.o
 OBJS-$(CONFIG_AVI_DEMUXER)               += avidec.o
-OBJS-$(CONFIG_AVI_MUXER)                 += avienc.o
+OBJS-$(CONFIG_AVI_MUXER)                 += avienc.o avlanguage.o
 OBJS-$(CONFIG_AVISYNTH)                  += avisynth.o
 OBJS-$(CONFIG_AVM2_MUXER)                += swfenc.o swf.o
 OBJS-$(CONFIG_AVR_DEMUXER)               += avr.o pcm.o