Upstreams the fix from #73310, so we can remove that patch.
Remove `infback.c` which we stopped compiling after #79273.
The `OF` macro was also removed so I can drop the patch where I yell
at Gentoo developers.
Security update, fixes CVE-2018-25032 in zlib.
Preliminary assessment doesn't show Godot as affected since we don't
seem to call `deflate` with the problematic parameters, but the extent
of the vulnerability is not fully clear upstream yet.
Rémi Verschelde