[llvm] [MISched] Make `getUnderlyingObjectsForInstr()` preserve unidentified objects (PR #225085)

[Nathan Corbyn via llvm-commits]

cofibrant wrote:

> AFAIU this is not a NFC, is it possible to test the change?

It depends on your definition of NFC. There are a few extra elements in the vector that are ignored at the only call site based on the return code, so the function changed but the compiler hasn't. 

https://github.com/llvm/llvm-project/pull/225085