clang-cl defines both __clang__ and _MSC_VER, yet uses `#pragma GCC` to disable certain diagnostics.

At the time `-Wreturn-type-c-linkage` was reported by clang-cl.
This PR fixes this behavior by reordering defines.

- avoid missing of necessary library dependencies

- Add special case handling when submodule has the same name as parent
- `PyDict_SetItemString` doesn't steal reference, so reference count
  should be explicitly decremented to transfer object life-time
  ownership
- Add sanity checks for module registration input

Comment from Python documentation:
Unlike other functions that steal references, `PyModule_AddObject()` only
decrements the reference count of value on success.
This means that its return value must be checked, and calling code must
`Py_DECREF()` value manually on error.

- weights are unaligned in dasiamprn sample (comes from numpy)

We only use that value as uint64_t below anyway.

* Use c++ namespaces explicitly

* Add root cv c++ namespace

- exceptions are catched by fallback CPU path
- OPENCV_OPENCL_ABORT_ON_BUILD_ERROR (disabled by default)