Unset DIRS after including subdir.mak so that the variable is not used

in the other subdirectory Makefiles.

Originally committed as revision 12801 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/Makefile

@@ -472,6 +472,8 @@ DIRS = alpha armv4l bfin i386 mlib ppc ps2 sh4 sparc
 
 include $(SUBDIR)../subdir.mak
 
+DIRS =
+
 $(SUBDIR)cpuid-test$(EXESUF): $(SUBDIR)i386/cputest.c
 $(SUBDIR)apiexample$(EXESUF): $(SUBDIR)apiexample.o $(SUBDIR)$(LIBNAME)
 $(SUBDIR)dct-test$(EXESUF): $(SUBDIR)dct-test.o fdctref.o $(SUBDIR)$(LIBNAME)