Rebasing of PRs

[Nicholas Wilson]

Some of you may have noticed that I have been merging a lot of 
Old PRs recently.

Due to some old CI bugs and other bitrot and PRs merged, many 
outstanding PRs need a rebase.

If you have an open PR in dmd or druntime marked `needs rebase` 
(if they're really old it may be better to close it and open a 
new one, it will be a long time before the CI gets to it) or a 
dlang.org PR that is not green, please do me a favour and rebase 
it and ping me when you do.

Many Thanks
Nic