Re: Improve const use in zlib-using code

Peter,

I like the idea. Though the way you have it implemented at the moment
seems like a trap in that any time zlib.h is included someone also has
to remember to add this define. I would recommend adding the define to
the build systems instead.

Since you put in the work to find the version of zlib that added this,
You might also want to add `required: '>= 1.2.5.2'` to the
`dependency('zlib')` call in the main meson.build. I am wondering if we
could remove the `z_streamp` check too. The version that it was added
isn't obvious.

--
Tristan Partin
Neon (https://neon.tech)