[llvm] Enable aggressive constant merge in GlobalMerge for AIX (PR #113956)

[via llvm-commits]

dyung wrote:

> > @syzaara your change is causing the test CodeGen/PowerPC/gcov_ctr_ref_init.ll to fail on several bots. Can you take a look and revert if you need time to investigate?
> 
> I merged a follow-up fix to the test: #114428

Ah yes, sorry I missed that. Thanks for the quick fix!

https://github.com/llvm/llvm-project/pull/113956