may fail to install on Windows with ALIEN_INSTALL_TYPE=share

I wasn't able to reproduce this:

https://gist.github.com/11cbbe72ab81a7e53eba5120bfd9c55e

While I'd like to see this fixed, at the moment, it may not in practice affect many users, since without ALIEN_INSTALL_TYPE set a successfully detected system install is the most likely scenario.
