[llvm] Merge sourcelocation in CSEMIRBuilder::getDominatingInstrForID. (PR #90922)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

This cannot change the public API of MachineIRBuilder. Constants are not intrinsically special. The same could happen for any CSE pair 

https://github.com/llvm/llvm-project/pull/90922