fix build of api_tests (#418)
fix build of api_tests (#418)

`tests/api/split_region.cpp` has a dependency on `utils.hpp` for
`ARRAY_SIZE`.
And `utils.hpp` has a dependency on `vulkan.h`. This header is not
always in the includes path, making the build fail.
kpet/clvk,kpet/clvk,kpet/clvk,kpet/clvk