title: What does `LinkingTo` do in an R package?
body: <p>I am building an R package whose description contains:</p>
  
  <pre><code>LinkingTo: Rcpp
  </code></pre>
  
  <p>The package has a fairly deep makefile structure. I know using <code>R CMD build .</code> creates and modifies variables such as <code>CXX11FLAGS</code> which must be passed down through subsequent layers of makefiles.</p>
  
  <p>I suspect that <code>LinkingTo</code> also produces such a variable, which I must be aware of and pass along. I suspect this because, several layers down, I hit the error:</p>
  
  <pre><code>mycode.hpp:5:10: fatal error: Rcpp.h: No such file or directory
  #include &lt;Rcpp.h&gt;
  </code></pre>
  
  <p>I'm not sure how to inform this file's makefile as to where Rcpp is. I suspect the hypothesized variable could be used, but I do not know that variable's name. Can anyone clarify?</p>