Deprecate support for ICC

[bernhardmgruber]

Intel's C++ Compiler Classic, frequently called ICC, has been deprecated by Intel for a while now and was ultimately dropped by the end of last year. Intel also stopped shipping it as part of oneAPI (cf. their ample hints in their documentation). To reduce our maintenance effort regarding additional workarounds needed here and there, which will likely increase when we move to newer C++ standards, I suggest to start deprecating ICC support and prepare for an eventual removal.

This could be as simple as issuing a warning during cmake configure, or when including CCCL headers, that support for ICC is deprecated and will be removed in the future.