[llvm] [ConstantMerge] Only merge constant w/unnamed_addr (PR #124050)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

#124220 is basically the right idea, yes.  Maybe we could do something more fancy, at least on ELF targets: if we make the external variable an alias for the internal variable, we can perform the merge without modifying either symbol's linkage.  (See GlobalMerge for an example of creating aliases like this.)

https://github.com/llvm/llvm-project/pull/124050