[lld] [llvm] [LLD][COFF] Add more `--time-trace` tags for ThinLTO linking (PR #156471)

[Alexandre Ganea via llvm-commits]

aganea wrote:

> lgtm but I think it would be good to change occurrences of "full LTO" and "regular LTO" in the description to something like the "LTO thin link" to avoid confusion, as those terms typically refer specifically to IR based LTO.

Are we talking about this tag?
<img width="1043" height="254" alt="Capture d’écran 2025-09-05 121607" src="https://github.com/user-attachments/assets/3e7f0720-5906-41e1-9863-e418728078dc" />

This codepath is also taken when Full LTO is used, right? (as in when `-flto` is used) I can conditionally change it to "LTO thin link (summary)" perhaps when ThinLTO is in effect? It's a bit confusing I find, becase we already have two others tags that say "ThinLink", one in `LTO::runThinLTO()` and one in `ThinLTOCodeGenerator::run()`. What would be a good naming for these three tags?

https://github.com/llvm/llvm-project/pull/156471