Fix test and add missing return for llvm-lto2 error case

Summary:
This test was missing the target triple.
Once I fixed that, the case with the invalid character error stopped
returning 1 from llvm-lto2 and the test reported a failure. Fixed by
adding the missing return from llvm-lto2. Apparently we were failing
when we eventually tried to get the target.

Reviewers: pcc

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D30585

llvm-svn: 297173