virglrenderer: 0.7.0 -> 0.8.1

freedesktop.org tarballs haven't been published since 0.7.0.  I've
sent a message to the mailing list (<87eev3cgcz.fsf@alyssa.is>),
suggesting newer tarballs be published.

Build system has changed from autoconf to meson+cmake/ninja, and the
vtest/util.c patch doesn't seem to be necessary any more.