[llvm] [Convergence] Extend cycles to include outside uses of tokens (PR #98006)

[Jay Foad via llvm-commits]

jayfoad wrote:

> When a convergence control token T defined at an operation D in a cycle
> C that is used by an operation U outside C, the cycle is said to be
> extended up to U.

Nit: remove "that" in the second line?

https://github.com/llvm/llvm-project/pull/98006