fixes several issues:
* `generic_address_space` test: add check for program scope variables.
The test uses both generic AS and program-scope variables, however it
only checked the generic-AS presence in `clGetDeviceInfo`.
* `compiler/test_compiler_defines_for_extensions.cpp`: add
`cl_khr_command_buffer_multi_device` to the list of recognized
extensions
* `command_buffer_event_sync.cpp`: add delays for testing
`clSetEventCallback` - according to specification, these can be executed
asynchronously (in a separate thread) by the OpenCL implementation,
hence the event callback is not quaranteed to be called before
`clFinish()` returns. Existing test `events/test_callbacks.cpp` also
waits for callback with loops of usleep.
* `images/kernel_image_methods/test_1D_buffer.cpp`: fix allocation size
being too small for the 1D buffer backing the image
---------
Co-authored-by: Ben Ashbaugh <ben.ashbaugh@intel.com>
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