stage2: implement `@prefetch`

This reverts commit f423b5949b8722d4b290f57c3d06d015e39217b0,
re-instating commit d48e4245b68bf25c7f41804a5012ac157a5ee546.
30efcf22d7Andrew Kelley committed on 1/18/2022, 6:59:09 PMparentf423b59
14 files changedLine totals unavailable