When DMD is used as a Dub dependency and generates the DMD version as
a pre generate command. Dub will execute this command in the current
working directory, which usually is the root package working directory,
instead of the DMD package directory. This will result in the wrong
version, that is, it will pick up the git tag of the root package
instead of the DMD package.
This looks related: https://github.com/dlang/dub/pull/659.
The Dub package was unconditionally running the `config.sh` shell
script to generate the `VERSION` file. A Bash shell script will not
work on Windows. Therefore the `config.sh` script has been ported to
D, which will work on both Windows and Posix.
