OpenCL API loading should be redesigned

[howetuft]

At the moment, the loading of the OpenCL API relies on a homemade wrangler ("CLEW") that is largely obsolete (2009).
This wrangler:

• is not maintained
• hard-codes the API search paths, in a list established 15 years ago, and may therefore be limited in finding this API
• may be unstable, especially if the API is not found
• does not take into account the different versions of OpenCL that have been released since its creation

A standard mechanism (OpenCL headers, ICD loader), maintained by Khronos, now exists to fulfil this function.
The wrangler should be replaced by this standard mechanism.

[CodeFHD]

I would add that the same applies to the CUDA extension wrangler "CUEW".