Update conf-libpng

[ddeclerck]

Summary of changes :

• use os-family instead of os-distribution to capture more derivatives
• Windows: use package libpng-devel instead of libpng, add os = "cygwin"
• Debian & Ubuntu: regroup Debian and Ubuntu, use libpng-dev for both, add os-family = "ubuntu" because some (many ?) Ubuntu derivatives (Linux Mint, elementaryOS, ...) only list Ubuntu in os-release:ID_LIKE (or list both, but Ubuntu first)

Add packages for :

• Mandriva and derivatives (same as Mageia)
• SUSE/OpenSUSE/SLES (note: no generic libpng-devel package, so use libpng16-devel)
• Fedora/RHEL/CentOS
• Alpine
• Arch Linux
• Gentoo and derivatives
• *BSD
• macOS

[ddeclerck]

I don't get why the CI fails on OpenSUSE 15.3. Works just fine with a fresh install in a VM.

[kit-ty-kate]

Thanks. Sorry for the wait

[ddeclerck]

Ah, I think you missed my previous comment about libpng-devel being provided by libpng16-compat-devel on OpenSUSE (i.e. zypper install libpng-devel works just fine).

[kit-ty-kate]

Ah sorry. Feel free to open a PR to add it back