I don't think rust-gcc will support Cargo, it will probably be the other way around. Generally, if you want to have an idea at how rust-gcc will look like and how it will be integrated into the wider ecosystem, you can take a look at gccgo, which is a GCC frontend for Go developed and supported by the core Go developers. However I don't have any experience with using it, so I can't tell you a lot about it besides that it exists...