In Meson better to use --werror option instead to manually add to
options.
Also this prevents build if spice-protocol deprecate some stuff
or fails the build if any warning occur.
This fixes an issue for
https://gitlab.freedesktop.org/spice/spice/-/issues/44.
Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Acked-by: Julien Ropé <jrope@gmail.com>