Draft: meson: override dependency provided as subproject
Meson 0.54.0 added a new method meson.override_dependency() that must be used to ensure dependency consistency.
This also has the effect that with Meson >0.54.0 an application depending on slirp can declare the fallback without knowing the dependency variable name: dependency('slirp').
Signed-off-by: Marc-André Lureau marcandre.lureau@redhat.com