[llvm] [lit] Echo full RUN lines in case of external shells (PR #65267)

[Petr Hosek via llvm-commits]

petrhosek wrote:

We saw the same issue on our bots as well, see for example:

https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-linux-x64/b8770760294040862593/overview

We did some investigation but haven't found the culprit either, but we saw trap faults in the kernel log.

https://github.com/llvm/llvm-project/pull/65267