
This patch allows zlib to compile cleanly with the -Wcast-qual gcc warning enabled, but only if ZLIB_CONST is defined, which adds const to next_in and msg in z_stream and in the in_func prototype. A --const option is added to ./configure which adds -DZLIB_CONST to the compile flags, and adds -Wcast-qual to the compile flags when ZLIBGCCWARN is set in the environment.