Feature: on Mac, Intel C++ is based on Apple Clang

[SSE4]

Changelog: Feature: Add Apple Clang as a base compiler for Intel C++.
Docs: conan-io/docs#1637

e.g. it allows -stdlib=libc++

related: #5699

reference:
https://software.intel.com/en-us/get-started-with-cpp-compiler-for-osx-parallel-studio-xe
https://software.intel.com/en-us/cpp-compiler-developer-guide-and-reference-stdlib

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^{Note: By default this PR will skip the slower tests and will use a limited set of python versions. Check here how to increase the testing level by writing some tags in the current PR body text.}

[danimtb]

This requires changes in the documentation at https://docs.conan.io/en/latest/reference/config_files/settings.yml.html

[SSE4]

docs: conan-io/docs#1637