[llvm] [CI] Make premerge_advisor_explain write comments (PR #166605)

[David Spickett via llvm-commits]

DavidSpickett wrote:

> The message is pretty much just "this test is failing at head" or "this test is flaky".

That's enough of an idea for me, I was mainly wondering how large it would get but now I think about it "failing at head" is all 99% of people would need to know anyway.

> Eventually we also want to propagate the build IDs as links, but we're leaving that for future work currently.

Build ID to the build where you found out that it was failing already you mean? Like "it's flaky at head (and here's the build that proves it)".

Cool idea but yes, "nice to have".

https://github.com/llvm/llvm-project/pull/166605