LLVM assertion failures hang with a modal dialog on Windows

[hkratz]

The Windows CI build with LLVM assertions enabled recently hung without an error message. It turned out to be an LLVM assertion failure resulting in a dialog which needed to be acknowledged, see #92535 (comment).

According to the assert documentation such a dialog is always displayed, but that is not the whole truth. Apparently _CrtSetReportHook() can be used to customize assertion failure handling. We should definitely make assertions failures exit with error after printing failure information to stderr instead of displaying a dialog and hanging.

@rustbot label O-windows

[Patrick-Poitras]

Could this be part of why we're getting so many hangs in the CI?

[hkratz]

@Patrick-Poitras That was responsible for four stuck dist-x86_64-msvc-alt builds recently. I don't think it was responsible for many timed out builds before that.

[ehuss]

Posted #93402 with a possible solution.