- Add (Csc/Vbc/Fsc)ToolExe environment variables when running Mono's MSBuild.
- Fix directory for the 'mono_assemblies_output_dir' argument being created with the '#' top level directory token as part of its name.
- Allow to build with 'mono_static=yes' on Unix without specifying a mono prefix. The build script will try to find the mono prefix using the output from pkg-config.