Windows build broken

[Andreas Klebinger]

Hi devs,

it seems the windows build is broken. (Can't build stage2 locally).

Quickest way to reproduce is a validate of master.

It also happens on CI: https://gitlab.haskell.org/ghc/ghc/-/jobs/270248

I remember ben mentioning something along the lines of builds with "old"
(8.6) boot compilers being broken.
Is that the culprint? How do I get back to a functioning environment?

Cheers,
Andreas