[clang] [clang][NFC] Increase NumStmtBits by 2 as we are approaching the limit (PR #120341)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Let's just increase to 9 bits.
> 
> Have you checked whether the size of `Stmt` or `Expr` changes when you do this?

I have these concerns as well, this ends up affecting the size of a lot of things....

That said, StmtNodes.td already has 267 items in it (as far as I can tell, just a wc -l on appearances of 'def').  So I don't know how we're getting away with this already.

Can you confirm how many are present currently? 

I also think 9 should be plenty, 512 should cover us for many many years.

https://github.com/llvm/llvm-project/pull/120341