Some OpenCL implementations may be broken, e.g. pocl simply
asserts and aborts if it can't find Clang. In order to protect
against crashes caused by faulty OpenCL drivers, when testing OpenCL
functionality on OpenCL setup change, first do a simple test
in a separate helper.

Change-Id: I1cf328e731c48f47745b27c7130e7521254209f5
Reviewed-on: https://gerrit.libreoffice.org/71080
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>