[llvm] [SelectionDAG] Treat CopyFromReg as freezing the value (PR #85932)

[Björn Pettersson via llvm-commits]

bjope wrote:

> I have had to revert this due to a test suite failure when compiling for AArch64 Scalable Vectors (SVE), for both specific vector lengths and length agnostic code.
> 

Thanks for the revert, and sorry for the inconvenience.
I'm working on a fix + re-apply.

https://github.com/llvm/llvm-project/pull/85932