title: clang++ via homebrew (llvm38) - compile error with system includes
body: <p>I'm using a Mac for development with 10.11.3</p>
  
  <p>Due to Apple llvm in Xcode 7 still not supporting openmp, I have used homebrew to install a more up to date llvm/clang that does support openmp via:</p>
  
  <pre><code>$ brew tap homebrew/versions
  $ brew install llvm38
  </code></pre>
  
  <p>I then have a very simple C++ test program, which is more or less a standard openmp test and which I know should compile:</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;omp.h&gt;
  
  int main(void)
  {
      #pragma omp parallel for
      for( unsigned v = 0; v &lt; 15; ++v )
      {
          printf("thread %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
      }
  }
  </code></pre>
  
  <p>Installing with homebrew, it suggests that you need to specify a few extra things to successfully compile, in particular, the path to the c++ system headers that were installed from the llvm38 package. This leads me to the following command line:</p>
  
  <pre><code>/usr/local/opt/llvm38/bin/clang++-3.8 -fopenmp openmp.cpp -stdlib=libc++ -nostdinc++ -I /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/ -L/usr/local/opt/llvm38/lib/llvm-3.8/lib
  </code></pre>
  
  <p>However, upon running this command, the compilation fails:</p>
  
  <pre><code>machine:tests me$ /usr/local/opt/llvm38/bin/clang++-3.8 openmp.cpp -stdlib=libc++ -nostdinc++ -I /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/ -L/usr/local/opt/llvm38/lib/llvm-3.8/lib
  In file included from openmp.cpp:1:
  In file included from /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/iostream:38:
  In file included from /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/ios:215:
  In file included from /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/iosfwd:90:
  /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/wchar.h:119:15: fatal error: 'wchar.h' file not found
  #include_next &lt;wchar.h&gt;
                ^
  1 error generated.
  </code></pre>
  
  <p>Does anyone know how to resolve this problem and get a successful compile?</p>