title: How can I deprecate a C++ header?
body: <p>I would like to deprecate a C++ header so that if someone includes it in their code, the compiler issues a warning.</p>
  <p>I know that I can deprecate individual symbols, for example, using C++14 <code>[[deprecated]]</code>, but is there a similar thing for headers? Maybe some clever trick?</p>
  <p>Note that I want the compiler to issue a warning even if the user doesn't use anything from the header.</p>