[llvm] [lit] Echo full RUN lines in case of external shells (PR #66408)

[via llvm-commits]

dyung wrote:

> > > > Can the test be restructured such that it can handle this?
> > > 
> > > 
> > > I'm concerned about weakening the test and missing other problems. I might use `grep -v` to throw away that line. Is that portable to windows?
> > 
> > 
> > I'm not sure. I think there are some tests that still do use grep, but I think the usage of it is highly discouraged these days.
> 
> I grepped for grep and found a number of tests still using it. I'll push a commit with this solution for now so that (hopefully) the bot is green again. We can try to find a better solution afterward. Does that seem reasonable?

Sure, that sounds reasonable to me.

https://github.com/llvm/llvm-project/pull/66408