Fix compilation as a win32 shared library (libavutil must be explicitly linked)

Originally committed as revision 19416 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale

libswscale/Makefile

@@ -5,6 +5,7 @@ NAME=swscale
 ifeq ($(BUILD_SHARED),yes)
 LIBVERSION=$(SWSVERSION)
 LIBMAJOR=$(SWSMAJOR)
+EXTRALIBS := -L../libavutil -lavutil$(BUILDSUF) $(EXTRALIBS)
 endif
 
 # NOTE: -I.. is needed to include config.h