Order matters, fix test files linking.

Originally committed as revision 25766 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/Makefile

 include $(SUBDIR)../config.mak
 
 NAME = avcodec
-FFLIBS = avutil avcore
+FFLIBS = avcore avutil
 
 HEADERS = avcodec.h avfft.h dxva2.h opt.h vaapi.h vdpau.h xvmc.h