By using a subproject, our own meson.build can use variables from
the subproject instead of hard-coded paths. This is also the first step
towards managing downloads with .wrap files instead of submodule.
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
c53648abba