Build-time bindgen requires that the geckoservo crate exist, both so
Cargo can have an accurate picture of the dependency graph and so we can
specify features to pass into it. Unfortunately, geckoservo won't exist
until the servo/servo import is done, which is going to take a little
while.
To land build-time bindgen on mozilla-central, therefore, we specify
this dummy geckoservo crate that does nothing. Our Rust code can then
depend on this crate, and things will magically continue to work when
the servo/servo import lands.
Nathan Froyd