clang (MSVC) kits should specify the 'ClangCL' toolset

[fredemmott]

Brief Issue Summary

Currently, the incorrect toolset 'host=amd64' is set (#2790) - as well as correcting 'amd64' to 'x64', ClangCL should be specified - e.g. toolset: "ClangCL,host=x64"

This makes CMAKE_CXX_COMPILER_ID and CMAKE_CXX_SIMULATE_ID bepopulated correctly ('Clang' and 'MSVC' respectively, and the MSVC variable remains correctly set to 1)

For example:

[
  {
    "name": "Custom Clang-CL from MSVC 2022 x64",
    "visualStudio": "ee13335b",
    "visualStudioArchitecture": "x64",
    "preferredGenerator": {
      "name": "Visual Studio 17 2022",
      "platform": "x64",
      "toolset": "ClangCL,host=x64"
    },
    "compilers": {
      "C": "C:\\Program Files\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\Llvm\\x64\\bin\\clang-cl.exe",
      "CXX": "C:\\Program Files\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\Llvm\\x64\\bin\\clang-cl.exe"
    }
  }
]

CMake Tools Diagnostics

No response

Debug Log

No response

Additional Information

Setting CMAKE_CXX_COMPILER_ID and CMAKE_CXX_SIMULATE_ID is useful to detect ClangCL within CMake; this is occasionally required when MSVC builds require a flag like /await:strict which errors with clang-cl.

[bobbrow]

Thank you for opening this issue. We should fix this in the same PR as the fix for #2790.

[fredemmott]

Another related note is the C and CXX compiler specifications do not appear to do anything when using clang-cl - for example, if I specify:

    "compilers": {
      "C": "C:\\Program Files\\LLVM\\bin\\clang-cl.exe",
      "CXX": "C:\\Program Files\\LLVM\\bin\\clang-cl.exe",
    }

... or specify CMAKE_CXX_COMPILER by hand in the CMakeCache.txt, when using the visual studio generators, cmake will always use the Visual-Studio-bundled clang-cl instead of the one I tell it to.

[bobbrow]

Another related note is the C and CXX compiler specifications do not appear to do anything when using clang-cl - for example, if I specify:

    "compilers": {
      "C": "C:\\Program Files\\LLVM\\bin\\clang-cl.exe",
      "CXX": "C:\\Program Files\\LLVM\\bin\\clang-cl.exe",
    }

... or specify CMAKE_CXX_COMPILER by hand in the CMakeCache.txt, when using the visual studio generators, cmake will always use the Visual-Studio-bundled clang-cl instead of the one I tell it to.

I opened a separate issue for this feedback since I already have a PR open for the original comment.