[llvm-branch-commits] [CI] Setup generate_report to describe ninja failures (PR #152621)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/152621

This patch makes it so that generate_report will add information about
failed build actions to the summary report. This makes it significantly
easier to find compilation failures, especially given we run ninja with
-k 0.

This patch only does the integration into generate_report (along with
testing). Actual utilization in the script is split into a separate
patch to try and keep things clean.