vf_pp: add postproc to the library dependencys for avfilter when enabled.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/Makefile

@@ -13,6 +13,7 @@ FFLIBS-$(CONFIG_ATEMPO_FILTER)               += avcodec
 FFLIBS-$(CONFIG_DECIMATE_FILTER)             += avcodec
 FFLIBS-$(CONFIG_MOVIE_FILTER)                += avformat avcodec
 FFLIBS-$(CONFIG_PAN_FILTER)                  += swresample
+FFLIBS-$(CONFIG_PP_FILTER)                   += postproc
 FFLIBS-$(CONFIG_REMOVELOGO_FILTER)           += avformat avcodec
 FFLIBS-$(CONFIG_MP_FILTER)                   += avcodec postproc
 FFLIBS-$(CONFIG_SMARTBLUR_FILTER)            += swscale