[SYCL][NFC] Fix skipping KernelBundleWith2Kernels test

[bader]

Currently most of unit tests print something and just return if test
pre-requisites are not met. llvm-lit reports such tests as "passed"
instead of "skipped" because Google Test framework reports test status
incorrectly. GTEST_SKIP must be used to indicate the framework "skipped"
test status.

Fixed a typo in PiMock.hpp.

TODO: the same approach must be applied to all other unittests.

[bader]

TODO: the same approach must be applied to all other unittests.

@intel/llvm-reviewers-runtime, I think we should rewrite unit-tests. They must be able to mock any device/platform and not skip the test based on default_selector behavior.
Thoughts?

[alexbatashev]

The reason why that wasn’t done earlier is that LLVM used an outdated version of Google Test library, that didn’t support skipping tests. We should update all of our tests, indeed.

[alexbatashev]

TODO: the same approach must be applied to all other unittests.

@intel/llvm-reviewers-runtime, I think we should rewrite unit-tests. They must be able to mock any device/platform and not skip the test based on default_selector behavior. Thoughts?

The problem with plugins is that they require external dependencies to be loaded properly. We need some sort of test plugin, that would assert when any of its APIs is called (or maybe simply set dispatch table entries to nullptr to get segfault). This plugin would not have any dependencies and would only be loaded when unit tests are run. Then we will no longer be able to write tests that rely on sycl::default_selector behavior.

[alexbatashev]

According to this page, there's an incident on github side, which affected testing results.