Merge commit 'a0ce85ac'

* commit 'a0ce85ac':
  configure: Globally add ZLIB_CONST to CPPFLAGS if zlib is enabled
Merged-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -5231,6 +5231,8 @@ for thread in $THREADS_LIST; do
     fi
 done
 
+enabled zlib && add_cppflags -DZLIB_CONST
+
 # conditional library dependencies, in linking order
 enabled aconvert_filter     && prepend avfilter_deps "swresample"
 enabled amovie_filter       && prepend avfilter_deps "avformat avcodec"