The only upstream change relative to the previous commit is that the
various Zcash-specific dependencies have been pulled into a cargo
workspace. The dependecies in the workspace use the same commits as the
crates we had previously vendored.
The patches are necessary to handle the fact that cargo requires that
dev dependencies are available even if not used, and we would otherwise
need to vendor all the underlying crates.
Add filename and SHA256 hash for Windows Rust package
When running `make download` in the `depends` directory, the `download-win` target (which `download` depends on) generates an error when it runs the commands defined in `check_or_remove_sources`:
```Makefile
sha256sum: /home/vagrant/zcash/depends/work/download/rust-1.16.0/..hash: no properly formatted SHA256 checksum lines found
funcs.mk:242: recipe for target '/home/vagrant/gitian-builder/cache/common/download-stamps/.stamp_fetched-rust-.hash' failed
make[1]: *** [/home/vagrant/gitian-builder/cache/common/download-stamps/.stamp_fetched-rust-.hash] Error 1
make[1]: Leaving directory '/home/vagrant/zcash/depends'
Makefile:153: recipe for target 'download-win' failed
make: *** [download-win] Error 2
```
The reason for the error is that `depends/packages/rust.mk` defines `rust_file_name_linux` and `rust_file_name_darwin` but leaves `rust_file_name_mingw32` undefined.
A directory of available rust downloads is here: https://static.rust-lang.org/dist/index.html
The closest windows analog in that list (using the same version number as currently defined in `rust.mk`) appears to be `rust-mingw-1.16.0-x86_64-pc-windows-gnu.tar.gz`. A corresponding sha256 value is also given in `rust-mingw-1.16.0-x86_64-pc-windows-gnu.tar.gz.sha256`.
After adding these values to `rust.mk`, the rust-mingw tar package was downloaded along with the rest of the dependencies and the above error message went away.
