title: Cannot use the C++ `std::filesystem` library with Meson build
body: <p>I am trying to build a piece of C++ code that uses the new C++17 Filesystem library, using the Meson build system.</p>
  
  <p>This is the piece of <code>meson.build</code> file involved:</p>
  
  <pre><code>if not compiler.has_header('filesystem')   # This is OK
      warning('The compiler has no &lt;filesystem&gt; header file')
  endif
  
  filesystem_dep = dependency('libc++fs', modules : ['filesystem'])
  
  test_exe = executable('test', test_src,
                        include_directories : include_dirs,
                        dependencies : filesystem_dep
                       )
  </code></pre>
  
  <p>In case the boost::filesystem library is used, this should be the correct syntax:</p>
  
  <pre><code>filesystem_dep = dependency('boost', modules : ['filesystem'])
  </code></pre>
  
  <p>How can I specify I want the version contained in the Standard C++ library? This is what I tried without success: 'libc++fs', 'stdlib', 'stdc++', 'libc++', 'c++', 'c++17'.</p>
  
  <p>This is the error message I get from Meson:</p>
  
  <blockquote>
    <p>src/meson.build:33:0: ERROR:  Native dependency 'libc++fs' not found</p>
  </blockquote>
  
  <p>The compiler I am currently using is LLVM/clang.</p>