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

[Ulrich Weigand via llvm-commits]

uweigand wrote:

Thanks for the tips.  I've managed to get the bot going again by clearing the build queues in the web interface, so it would reset to current mainline.   All s390x bots are now green again.

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