[CUDA] Fix faulty test from rL288448

Summary:
The test introduced by rL288448 is currently failing because
unimportant but unexpected errors appear as output from a test compile
line. This patch looks for a more specific error message, in order to
avoid false positives.

Reviewers: jlebar

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D27328

Switch to more specific error