TruffleRuby provides the zlib module but not the native zlib system
library that the module uses.
On all Linux distributions we have tested, zlib is always going to be
installed by other packages that you need to install, so we have never needed to
install it manually.
On macOS the system version can be used.
If zlib is in a non-standard location for your system, you can use the
option:
-Xcexts.remap=libz.so:path/to/libz.so