Later versions of Rust include the Rust architecture in the output
directory by default (i.e i686-pc-windows-msvc or
x86_64-pc-windows-msvc), so we must include that in the output path in
both the NMake Makefile that is used to call cargo, as well as in the
rsvg-rust project, so that the librsvg DLL can properly link, and to
avoid running Cargo again when the Rust portion has been successfully
built.