[llvm] [AliasSetTracker] Use ModRefInfo (NFC) (PR #217917)

[Nikita Popov via llvm-commits]

nikic wrote:

> LGTM, assuming this was not done to avoid pulling in the entire ModRef.h.

I believe it was done because AST predates the existence of ModRefInfo :)

https://github.com/llvm/llvm-project/pull/217917