[llvm] [DebugInfo][RemoveDIs] Use iterators to insert everywhere (PR #102003)

[Jeremy Morse via llvm-commits]

jmorse wrote:

This is unexpectedly slowing -O3 builds a little bit: https://llvm-compile-time-tracker.com/compare.php?from=1139dee910c45cfdd4a6066b22addef585e04032&to=fd7d7882e7fa5a38d4bfde426120d4663718beb4&stat=instructions%3Au

Which is especially unexpected seeing how it's a tiny number of call sites that shouldn't reeeaaalllyyy be behaving any differently. One wonders if it's some second-order inlining thing. I'll examine a little shortly.

https://github.com/llvm/llvm-project/pull/102003