search for LLVM clang-cl compiler

[elahehrashedi]

bugfix: #2622

a sample clang kit:

  {
    "name": "Clang 12.0.0 (MSVC CLI) for MSVC 16.11.32602.291 (Visual Studio Enterprise 2019 Release - x86)",
    "visualStudio": "dc3c7e8c",
    "visualStudioArchitecture": "x86",
    "preferredGenerator": {
      "name": "Visual Studio 16 2019",
      "platform": "x86",
      "toolset": "host=x86"
    },
    "compilers": {
      "C": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise\\VC\\Tools\\Llvm\\bin\\clang-cl.exe",
      "CXX": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise\\VC\\Tools\\Llvm\\bin\\clang-cl.exe"
    }
  }