* Add memory_scope_all_devices testing
This duplicats memory_scope_all_svm_devices testing, but it seems pretty quick
so I don't think it hurts.
Fixes#990
* Address clang-format failures
* Address a further clang-format failure
* Change setup code in `KernelCode()` to use `_explicit` builtin
variants that are common to both OpenCL-2.X and OpenCL-3.0.
* Only test optional supported builtin variants (`_explicit` signature
memory_order/scope) for OpenCL-3.0.
* Disable program scope global variable and generic address space tests
for a OpenCL-3.0 driver which does not optionally support these
features.
