[clang] [LifetimeSafety] Add bailout for large CFGs (PR #170444)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

> I also wonder if it is better to do something else for functions with large CFGs. E.g., instead of entirely skipping them, we could just visit all nodes ones and not iterate to a fixed-point.

I have tried doing that earlier to reduce improve performance on LLVM but had no success. The primary bottleneck in practice seems to be the number of join operations we need to do even in a single iteration and this is proportional to the number of blocks. 
I would recommend to not do anything more clever here. Set this limit relatively high would make almost all human-written code in the scope of the analysis.

https://github.com/llvm/llvm-project/pull/170444