PHP bindings for libvirt virtualization toolkit Formula was removed
Last version was
php56-libvirt requires the following formulae to be installed:
autoconf 2.69 Automatic configure script builder
pkg-config 0.29.2 Manage compile and link flags for libraries
libvirt 4.2.0 C virtualization API

Recent formula history

ilovezfs php56: migrate to homebrew/core (#4835)
ilovezfs php56-libvirt: bottle revision to rebuild.
Andreas Braun Add description for libvirt formula
Andy Blyler fix style issues
Andy Blyler php56-libvirt: convert from sha1 to sha256

Formula code at GitHub