Environment variables are not serialized during configuration

This makes the VS backend unwieldy to use as you set various variables such as `LIB` and `INCLUDE` will be lost the second another tool in its own environment be it `msbuild` or Visual Studio try to regenerate the build and then regeneration will fail.

Start by tracing the VS backend's configuration and regeneration handling for environment variables such as LIB and INCLUDE. Reproduce regeneration through msbuild or Visual Studio, then determine where those variables are lost. Done means the variables survive regeneration and the build no longer fails.

Written by the indexing model from the issue text.