Fix gif encoder dependencies

Originally committed as revision 21986 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/Makefile

@@ -127,7 +127,7 @@ OBJS-$(CONFIG_FOURXM_DECODER)          += 4xm.o
 OBJS-$(CONFIG_FRAPS_DECODER)           += fraps.o huffman.o
 OBJS-$(CONFIG_FRWU_DECODER)            += frwu.o
 OBJS-$(CONFIG_GIF_DECODER)             += gifdec.o lzw.o
-OBJS-$(CONFIG_GIF_ENCODER)             += gif.o
+OBJS-$(CONFIG_GIF_ENCODER)             += gif.o lzwenc.o
 OBJS-$(CONFIG_H261_DECODER)            += h261dec.o h261.o \
                                           mpegvideo.o error_resilience.o
 OBJS-$(CONFIG_H261_ENCODER)            += h261enc.o h261.o             \