[llvm] [NFC][RemoveDIs] Switch constant-hoisting to insert with iterators (PR #84738)

[Orlando Cazalet-Hyams via llvm-commits]

https://github.com/OCHyams approved this pull request.

> I've sent this up to the compile time tracker to see whether there's a major cost from this.

LGTM, pending those results

https://github.com/llvm/llvm-project/pull/84738