[OpenCL] In test/Driver/opencl.cl, don't require name of Clang binary to contain "clang"

The test currently fails if the name of the Clang binary doesn't contain "clang".

This patch removes that requirement, as some environments may choose to run the test with a differently named binary. This shouldn't make the test any less strict -- the only place where the flags we're searching for can really occur is the Clang command line.

Patch by Martin Böhme!

Differential Revision: https://reviews.llvm.org/D22359

llvm-svn: 275428