title: Building Boost with Clang "Failed to build Boost.build engine"
body: <p>I am trying to build Boost 1_74_0 for Clang on Windows 7. I go to the folder with bootstrap etc and run:</p>
  
  <p><code>bootstrap --with-toolset=clang-win</code></p>
  
  <p>but I get:</p>
  
  <pre><code>Building Boost.build engine
  Failed to build Boost.build engine
  </code></pre>
  
  <p>and the log says:</p>
  
  <pre><code>Found with vswhere Visual Studio Locator version 2.5.2+gebb9f26a3d
  ###
  ### "Unknown toolset: vcunk"
  ###
  ### You can specify the toolset as the argument, i.e.:
  ###     .\build.bat msvc
  ###
  ### Toolsets supported by this script are: borland, como, gcc,
  ###     gcc-nocygwin, intel-win32, metrowerks, mingw,
  ###     vc11, vc12, vc14, vc141, vc142
  </code></pre>
  
  <p>I did add my Clang bin folder to my PATH env variable.</p>
  
  <p>How should I resolve this?</p>