Skip compiler unload/reload tests if compiler is not available (#986)

* Skip compiler unload/reload tests if compiler is not available

Note that tests that use the compiler helper functions but won't work without a
compiler are in the `subtests_to_skip_with_offline_compiler` list.  I didn't do
that here because they tests directly use `clBuildProgram` etc directly,
because they're specifically testing it's behaviour in edge-cases.

* Change type of status variable
4 files changed