* meson.build: Fix zlib support.

This commit synchronizes zlib support with both autotools and cmake: If no
external zlib is found (or intentionally disabled on the command line), use
the internal zlib by undefining `FT_CONFIG_OPTION_SYSTEM_ZLIB` without
modifying `FT_CONFIG_OPTION_USE_ZLIB`.

Also improve summary output.

Problem reported by Moazin.
1 file changed