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

[Jinsong Ji via llvm-commits]

jsji wrote:

Looks like this PR might cause unexpected failure in testing, and kill buildbot worker (also python code). Examples can be found: https://lab.llvm.org/buildbot/#/builders/184/builds/6236.
https://lab.llvm.org/buildbot/#/builders/197/builds/9358

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