[Bug] modules zsh/tcp, zsh/zftp unloadable, probably affecting most modern Linuxes

[Marcus Müller <marcus_zsh@xxxxxxxxxxx>]

Dear ZSH community,

I just opened a Fedora bug[1], since I suspected this to a configuration-vs-facts mistake 
in the build, but it turns out that this happens on debian, too, and that I can see in the 
source code that the offending function is actually used – which should have made linkage 
fail, but it only does so at dynamic runtime linking.

Don't really know how to go from there – someone would have to rework name resolution to 
use getaddrinfo/freeaddrinfo (which is POSIX) instead of getipnodebyname/freehostent 
(which isn't POSIX).

I see that this already happened, in 2007, in commit 
a5187bb6ac96cc43f68367c5dc9332854c250713, "23670: use getaddrinfo() and getnameinfo() 
instead of get*by* functions.", but was promptly reverted 30 minutes later without 
explanation. Maybe it's time to revisit that? Maybe it's also just a sign that the code 
hasn't been used by anyone in roughly forever, and deserves to be not built on the 
platforms it doesn't support, or removed altogether.

Bug description:

when running `zmodload zsh/zftp`, it fails due to missing symbol `freehostent`. This is 
worrisome, because a) that's a broken feature, and b) `freehostent` shouldn't be used on 
glibc systems (far as I can tell) – `man freehostent` tells us that the function is *not* 
present in glibc and deprecated.

Steps to Reproduce:
1. clean F37 or F38 or debian stable installation
2. `sudo dnf --refresh install -y zsh`
3. `zsh`
4. in zsh: `zmodload zsh/zftp`

Actual Results:
zsh: failed to load module `zsh/zftp': /usr/lib64/zsh/5.9/zsh/zftp.so: undefined symbol: 
freehostent

Expected Results:
loading of module

Best regards,
Marcus Müller


[1] https://bugzilla.redhat.com/show_bug.cgi?id=2212160