Add support for meson

A few 7 year old patches that never made it upstream, followed by some cleanups and support for meson. Building XIT now just comes down to

$ git submodule init
$ git submodule update
$ meson build && ninja -C build test

Some tests fail, but they do with the autotools build too, so...

Reverts the tuple patch because of #1 (closed)

cc @p12tic

Requires xorg-gtest!4 (merged)