[llvm-branch-commits] [CI] Enable Build Failure Reporting (PR #152622)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/152622

This patch finishes up the plumbing so that generate_test_report will dump build
failures into the Github checks summary.