At the time of writing, most Linux distributions ship their PHP versions with sockets enabled by default.
CentOS 7, PHP 5.4: Enabled;
CentOS 7, Remi repo, PHP 7.1.1: Enabled;
CentOS 7, DirectAdmin Custombuild, PHP 7.0.9: Enabled;
CentOS 7, DirectAdmin Custombuild, PHP 5.6.24: Enabled;
Debian Jessie, PHP 5.6.30-0+deb8u1: Enabled;
Gentoo Linux ~amd64, PHP 7.1.1: Enabled (USE-flag "sockets" is enabled by default)
Alpine Linux: PHP 5.6.30: Disabled, however this can simply be enabled by installing php5-sockets
I haven't tested other distros/versions, but as far as compatibility goes most systems seem to support sockets out of the box.