Fix Windows ninja builds when MAX_JOBS is specified (#65444)
Summary:
Reported by cloudhan in https://github.com/pytorch/pytorch/pull/64733#issuecomment-924545463
Fixes regression introduced by https://github.com/pytorch/pytorch/commit/047e68235f8ebf8dc9fd816829ba90561d423ff9
cc malfet seemethere
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65444
Reviewed By: dagitses, seemethere
Differential Revision: D31103260
Pulled By: malfet
fbshipit-source-id: 9d5454a64cb8a0b96264119cf16582cc5afed284
