libvhost-user: make it a subproject (was: "lower dependency on QEMU headers") Hi, libvhost-user is meant to be free of glib dependency, and easily copyable/reusable outside of QEMU. Clean-up some dependencies that crept in recently (the one remaining is qemu/atomic.h, from which a subset is used) v2: - fix memfd flags argument (spotted by D. Gilbert) - new patches to remove dependency from QEMU headers - make it a standalone meson subproject - check subproject build in gitlab CI (suggested by S. Hajnoczi) - add some r-b tags