[llvm] Add a pass to collect dropped variable statistics (PR #102233)

[Shubham Sandeep Rastogi via llvm-commits]

rastogishubham wrote:

@adrian-prantl @jmorse @jryans just pinging again to see if there were any other changes or is this patch good to go in

https://github.com/llvm/llvm-project/pull/102233