[llvm] [Reassociate] Use a reference to DataLayout instead of copying the underlying string data (NFC) (PR #128269)

[Nikita Popov via llvm-commits]

nikic wrote:

> In a follow-up i'm tempted to make the DataLayout copy constructor private, to avoid this in future. There are a few tests which copy the DataLayout, and perhaps need to (I didn't check yet), but we could provide a clone() method for them if needed. Its only accidental copying I think we should consider avoiding, not people who really do need to copy it for reasons.

Maybe making the copy construct explicit would be good enough?

https://github.com/llvm/llvm-project/pull/128269