* 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
* add test_compiler test for OpenCL C versions
* add checks for required OpenCL C versions
* bugfix: only OpenCL C 2.0 is required for OpenCL 2.1 and 2.2
* pass reference to feature struct vs. pointer
* address review comments regarding C++ identifiers and 3d image writes
* Test feature macro OpenCL 3.0
* Test feature macro OpenCL 3.0 - refactor to template function
* Use test_error and format fix issues
* Fix returned value type for CL_DEVICE_MAX_GLOBAL_VARIABLE_SIZE
* Code format fix
* Feature macro test - refactor code to have one test case
* add consistency checking comparing supported features to CL_DEVICE_OPENCL_C_FEATURES
* fix minor issues
* Feature macro test - fix test version
* Feature macro test - add -cl-std=CL3.0 build option
* Feature macro test - compilation errors
* Feature macro test - compilation errors OSX
* Feature macro test - fix adding build options
* Feature macro test - share function OutputBuildLogs
* Feature macro test - back removed cases
* Feature macro test - review fixes
* Feature macro test - split check image formats
* Feature macro test - fixed version
