libavformat: Fix standalone compilation of the webm muxer

The missing object file was added to the matroska muxer already, but
not to the webm muxer.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/Makefile

@@ -329,7 +329,7 @@ OBJS-$(CONFIG_WAV_MUXER)                 += wavenc.o
 OBJS-$(CONFIG_WC3_DEMUXER)               += wc3movie.o
 OBJS-$(CONFIG_WEBM_MUXER)                += matroskaenc.o matroska.o \
                                             isom.o avc.o \
-                                            flacenc_header.o avlanguage.o
+                                            flacenc_header.o avlanguage.o wv.o
 OBJS-$(CONFIG_WSAUD_DEMUXER)             += westwood_aud.o
 OBJS-$(CONFIG_WSVQA_DEMUXER)             += westwood_vqa.o
 OBJS-$(CONFIG_WTV_DEMUXER)               += wtv.o asfdec.o asf.o asfcrypt.o \