title: How to add include path on Ninja and clang for VS 2019?
body: <p>So, I want to build my project with additional include path using CMake and clang as a frontend for VS2019. </p>
  
  <p>What I already try:</p>
  
  <ul>
  <li>CMakeLists.txt</li>
  </ul>
  
  <pre><code># CMakeList.txt : CMake project for test-llvm, include source and define
  # project specific logic here.
  #
  cmake_minimum_required (VERSION 3.8)
  
  # Add source to this project's executable.
  add_executable (test-llvm "test-llvm.cpp" "test-llvm.h")
  
  # TODO: Add tests and install targets if needed.
  set(INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/include")
  </code></pre>
  
  <ul>
  <li>CMakeSettings.json</li>
  </ul>
  
  <pre><code>{
    "configurations": [
      {
        "name": "x64-Clang-Debug",
        "generator": "Ninja",
        "configurationType": "Debug",
        "buildRoot": "${projectDir}\\out\\build\\${name}",
        "installRoot": "${projectDir}\\out\\install\\${name}",
        "cmakeCommandArgs": "",
        "buildCommandArgs": "-v",
        "ctestCommandArgs": "",
        "inheritEnvironments": [ "clang_cl_x64" ],
        "variables": []
      },
      {
        "name": "x86-Clang-Release",
        "generator": "Ninja",
        "configurationType": "RelWithDebInfo",
        "buildRoot": "${projectDir}\\out\\build\\${name}",
        "installRoot": "${projectDir}\\out\\install\\${name}",
        "cmakeCommandArgs": "",
        "buildCommandArgs": "-v",
        "ctestCommandArgs": "",
        "inheritEnvironments": [ "clang_cl_x86" ],
        "variables": []
      }
    ]
  }
  </code></pre>
  
  <ul>
  <li>test-llvm.cpp</li>
  </ul>
  
  <pre class="lang-cpp prettyprint-override"><code>#include &lt;needtoinclude.h&gt;
  
  int main()
  {
      std::cout &lt;&lt; "Hello world" &lt;&lt; std::endl;
  }
  </code></pre>
  
  <ul>
  <li>test-llvm.h (Empty)</li>
  </ul>
  
  <pre class="lang-cpp prettyprint-override"><code>
  </code></pre>
  
  <ul>
  <li>include/needtoinclude.h</li>
  </ul>
  
  <pre class="lang-cpp prettyprint-override"><code>#pragma once
  #include &lt;iostream&gt;
  </code></pre>
  
  <p>And which <strong>errors</strong> I get:</p>
  
  <pre><code>&gt;------ Build All started: Project: test-llvm, Configuration: x64-Clang-Debug ------
    [1/2] C:\PROGRA~2\MIB055~1\2019\PROFES~1\COMMON7\IDE\COMMON~1\MICROS~1\Llvm\bin\clang-cl.exe  /nologo -TP   -m64 -fdiagnostics-absolute-paths  /DWIN32 /D_WINDOWS /W3 /GR /EHsc /MDd /Zi /Ob0 /Od /RTC1 /showIncludes /FoCMakeFiles\test-llvm.dir\test-llvm.cpp.obj /FdCMakeFiles\test-llvm.dir\ -c ..\..\..\test-llvm.cpp
    FAILED: CMakeFiles/test-llvm.dir/test-llvm.cpp.obj 
    C:\PROGRA~2\MIB055~1\2019\PROFES~1\COMMON7\IDE\COMMON~1\MICROS~1\Llvm\bin\clang-cl.exe  /nologo -TP   -m64 -fdiagnostics-absolute-paths  /DWIN32 /D_WINDOWS /W3 /GR /EHsc /MDd /Zi /Ob0 /Od /RTC1 /showIncludes /FoCMakeFiles\test-llvm.dir\test-llvm.cpp.obj /FdCMakeFiles\test-llvm.dir\ -c ..\..\..\test-llvm.cpp
  C:\Users\stakemura\Dropbox\Documents\test-llvm\test-llvm.cpp(1,13): fatal error : 'needtoinclude.h' file not found
    &lt;U+FEFF&gt;#include &lt;needtoinclude.h&gt;
                     ^~~~~~~~~~~~~~~~~
    1 error generated.
    ninja: build stopped: subcommand failed.
  
  Build All failed.
  </code></pre>
  
  <p>How should I do to add include path?</p>