title: Vim YouCompleteMe c++17 : warning on decomposition declaration
body: <p>I would like to set YouCompleteMe correctly so that I do not get the following warning on a c++ file:</p>
  
  <pre class="lang-cpp prettyprint-override"><code>...
  
  auto [k,v] = mapIt; // some map iterator
  
  ...
  </code></pre>
  
  <pre><code>decomposition declarations are a C++17 extension
  </code></pre>
  
  <p>I added </p>
  
  <pre><code>   flags.append( '-std=c++17' ) 
  </code></pre>
  
  <p>in</p>
  
  <pre><code>~/.vim/bundle/YouCompleteMe/third_party/ycmd/.ycm_extra_conf.py
  </code></pre>
  
  <p>and added the following to</p>
  
  <pre><code>~/.vimrc
  </code></pre>
  
  <pre><code>let g:ycm_global_ycm_extra_conf = '~/.vim/bundle/YouCompleteMe/third_party/ycmd/.ycm_extra_conf.py'
  </code></pre>