reduce compiler warnings and stderr noise
[#101341]amigaos4: cpan/Compress-Raw-Zlib: also amigaos4
[#106799]const all global data
https://github.com/madler/zlib/commit/82e9dc60932bf2ce5422a5e76e66e5a05abd26e3
[#101298]Coverity finding: Unused value
https://github.com/madler/zlib/commit/9859a94c1002484ee5f824c05683a5b2484cbf49
[105414]Coverity findings
[102399]Coverity finding: Overlapping buffer in memory copy
[105413]