[llvm] [RISCV] Enable merging of external globals by default (PR #117880)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM.

Thank you for the performance data.  I agree the performance is pretty much in the noise, but this makes sense in concept.  Given that, I think moving forward here is the right answer.  

https://github.com/llvm/llvm-project/pull/117880