Auto merge of #103392 - RalfJung:miri, r=oli-obk

update Miri

I had to use a hacked version of josh to create this, so let's be careful with merging this and maybe wait a bit to see if the josh issue becomes more clear. But the history looks good to me, we are not adding duplicates of rustc commits that were previously mirrored to Miri.

Also I want to add some cross-testing of Miri in x.py.