rather than prepend it.
This way there is the guarantee that the included headers are those in
the FFmpeg sources, rather than pre-installed headers referenced by
the user CPPFLAGS.
Originally committed as revision 19416 to svn://svn.ffmpeg.org/ffmpeg/trunk
ALLFFLIBS = avcodec avdevice avfilter avformat avutil postproc swscale
-CPPFLAGS += -DHAVE_AV_CONFIG_H -I$(BUILD_ROOT_REL) -I$(SRC_PATH)
+CPPFLAGS := -DHAVE_AV_CONFIG_H -I$(BUILD_ROOT_REL) -I$(SRC_PATH) $(CPPFLAGS)
%.o: %.c
$(CC) $(CPPFLAGS) $(CFLAGS) $(LIBOBJFLAGS) -c $(CC_O) $<