Use $^ without header files instead of $(SRCS) to reference the dependencies

of the .depend target. $^ apparently includes the full path to files found
in a vpath directory, $(SRCS) does not. This makes out of tree builds fail.

Originally committed as revision 12421 to svn://svn.ffmpeg.org/ffmpeg/trunk

Makefile

@@ -223,7 +223,7 @@ depend dep: .depend .vhookdep
 	$(MAKE-$(CONFIG_AVFILTER)) -C libavfilter depend
 
 .depend: $(SRCS) version.h
-	$(CC) -MM $(CFLAGS) $(SRCS) > $@
+	$(CC) -MM $(CFLAGS) $(filter-out %.h,$^) > $@
 
 # gcc stupidly only outputs the basename of targets with -MM
 .vhookdep: $(ALLHOOKS_SRCS) version.h