Clear some more variables that are used on subdir Makefiles.

Originally committed as revision 18180 to svn://svn.ffmpeg.org/ffmpeg/trunk

Makefile

@@ -47,7 +47,8 @@ $(PROGS): %$(EXESUF): %_g$(EXESUF)
 	cp -p $< $@
 	$(STRIP) $@
 
-SUBDIR_VARS := OBJS FFLIBS CLEANFILES DIRS TESTPROGS EXAMPLES
+SUBDIR_VARS := OBJS FFLIBS CLEANFILES DIRS TESTPROGS EXAMPLES \
+               ALTIVEC-OBJS MMX-OBJS YASM-OBJS-FFT YASM-OBJS
 
 define RESET
 $(1) :=