Test matrix

We support a lot of configuration options (probably too many), compilers, OpenCL versions etc with these bindings; definitely too many to test all combinations exhaustively. The testing we have currently is however pretty weak. The purpose of this issue is to gather feedback on the configurations that we do need to test to try and find a sweet spot. Here's a list of the variables with values we may want to test:

Compilers:
* GCC
* Clang
* MSVC

OpenCL versions:
* OpenCL 1.0
* OpenCL 1.1
* OpenCL 1.2
* OpenCL 2.0
* OpenCL 2.1
* OpenCL 2.2

Operating systems:
* Linux
* Windows
* MacOS

Configuration options:
* `CL_HPP_ENABLE_EXCEPTIONS`
* More?

C++ versions:
* C++ 11
* C++ 14
* C++ 17
* C++ 20

Anything to add/remove?

Start by reviewing the configuration and existing testing setup for OpenCL-CLHPP, then compare the listed compilers, OpenCL versions, operating systems, C++ versions, and CL_HPP_ENABLE_EXCEPTIONS option against what is currently covered. Done means agreeing on a practical test matrix and documenting or implementing the resulting coverage, but the issue does not name specific files or tests.

Written by the indexing model from the issue text.