[llvm] [Pipelines] Perform mergefunc after constmerge (PR #92498)

[YAMAMOTO Takashi via llvm-commits]

yamt wrote:

> Can you please add a test in llvm/test/Transforms/PhaseOrdering (e.g. with `-O2 -enable-merge-functions`)?

i added a few tests.


https://github.com/llvm/llvm-project/pull/92498