hadrian: Expose wrapper executable for GHCi on Windows
This fixes #18761 (closed) by teaching Hadrian to build the ghci
wrapper executable in driver/ghci
on Windows. As described on the ticket, this will require revisiting in %9.2.1 since it currently doesn't handle the case of relocatable builds on non-Windows platforms. Nevertheless, this is at least enough to get %9.0.1 unstuck.