VS: Support Visual Studio Clang Toolkit identification
Adds support for the Visual Studio Clang tookit so the clang compiler is properly identified when the toolset is ClangCl (e.g. -T or CMAKE_GENERATOR_TOOLSET).
Topic-rename: vs-clangcl-toolset
Adds support for the Visual Studio Clang tookit so the clang compiler is properly identified when the toolset is ClangCl (e.g. -T or CMAKE_GENERATOR_TOOLSET).
Topic-rename: vs-clangcl-toolset