[llvm] [InlineCost] Enable the cost benefit analysis for Sample PGO (PR #66457)

[Xiangyang Guo via llvm-commits]

helloguo wrote:

When we test cost-benefit on our internal workloads, we see 0.4-0.5% regressions on several workloads. Even after we tune the related flags (e.g.-inline-savings-multiplier), we still see some gap between cost-benefit vs cost-threshold. While cost-benefit seems reasonable, the effectiveness also depends on other factors such as profile quality. 

https://github.com/llvm/llvm-project/pull/66457