[llvm] [PGO] Gracefully handle zero entry-count in `fixFuncEntryCount` (PR #112029)

[via llvm-commits]

https://github.com/WenleiHe commented:

Beyond the point fix here, I'm wondering if we want to consider profile inference to smooth the counts for sampled IRPGO just like HW sample PGO. @xur-llvm wdyt? 

https://github.com/llvm/llvm-project/pull/112029