build: make doc generation work on Windows

PR-URL: https://github.com/nodejs/node/pull/22749
Refs: https://github.com/nodejs/node/pull/21697


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>