[bugpoint] Avoid noisy errors by passing a valid opt to tests

If the tests don't use the in-tree opt, we're liable to see some silly
error messages due to the version mismatch (missing flags, etc).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324703 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed