[feature] Improve Clang runtime management

[franramirez688]

Clang has this definition of runtime in our settings.yml:

    clang:
        ...
        runtime: [None, MD, MT, MTd, MDd]

We're not managing properly these runtime flags and we should do the same as for Visual Studio case because it's confusing you can use it but Conan is doing nothing.

Original issue: #9537

• I've read the CONTRIBUTING guide.

[franramirez688]

In the end, this issue does not make sense for clang but clang-cl (that's another issue because it's managed in a different way). The question is if we should get rid of this compiler.runtime setting for Conan 2.0 because it is not being used so far.