Fix an assert failure for CAS with include tree and vfs overlay

[hjyamauchi]

#11616

[hjyamauchi]

@swift-ci please test

[hjyamauchi]

@swift-ci please test Windows platform

[cachemeifyoucan]

Does it happen on next branch?

This change will not apply to next since VFS layer is free of CAS representation now. If next is fine, I can cherry-pick over the CAS changes from next branch. Otherwise, we need a different fix.

[hjyamauchi]

Yes, this crashes on the next branch too.

I see that after #11235, the fix doesn't work.

Do you have a suggestion how we may fix this on next? I didn't come up with a good way there because FileWithFixedStatus isn't visible outside VirtualFileSystem.cpp and the dyn_cast<CASBackedFile> checks do not seem to straightforwardly fit with the FileWithFixedStatus case.

[cachemeifyoucan]

Yes, this crashes on the next branch too.

I see that after #11235, the fix doesn't work.

Do you have a suggestion how we may fix this on next? I didn't come up with a good way there because FileWithFixedStatus isn't visible outside VirtualFileSystem.cpp and the dyn_cast<CASBackedFile> checks do not seem to straightforwardly fit with the FileWithFixedStatus case.

Let me try your test case on next branch.

[cachemeifyoucan]

#11629

[hjyamauchi]

#11629

Great. What do we do for the stable/21.x branch?