So it seems I misunderstood the concept of a bare regex literal, thanks for pointing out.
Regex literals are not understood by Swift compiler on Windows due to missing bootstrapping step (I’m surprised that this is an enabled feature because Implementing Parts of the Swift Compiler in Swift was posted long after Swift 5.7 branch cut-off).
To try getting it enabled, we may need to enable bootstrapping without SIL optimization module. Not sure if it’s supported now.