[test-suite] Signal error if llvm-lit was not found

I'm not sure if that was intentional or not?
I found it quite surprising when trying to integrate a new external project.

Reviewers: MatzeB, homerdin, hfinkel

Reviewed By: hfinkel

Subscribers: mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60091

git-svn-id: https://llvm.org/svn/llvm-project/test-suite/trunk@364388 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed