Add ''set working directory" option to shimgen generation itself

[dvht]

The only way to have a shimgen started in its own directory is by adding --shimgen-usetargetworkingdirectory to the command line options when starting the shim. This means you will have to provide a scriptl which adds this option + the other command line arguments.
One of the advantages of shim is not needing those wrapper scripts, which mess up quotes and spaces.
Passing "-c --shimgen-usetargetworkingdirectory" to shimgen itself, does not work. It passes the argument without evaluating it.