Linking error when building rust crate in debug mode on Windows

[zaddach]

The rust crate fails to build on Windows because the C++ libraries are trying to link to the debug vc runtime (/MDd), whereas Rust always links against the release runtime (/MD), even when building debug configuration.

Release builds fine.

[benjaminwinger]

This should probably be documented, but we've been setting /MDd via environment variables in the Makefile here, which has been working, so it is possible (Also see rust-lang/rust#39016 (comment)). However I can also understand if that's not a reliable solution for your workflow.