title: clang compiler options aren't documented?
body: <p>For the sake of migrating compiler options to ARM using Xcode, I'm looking for a comprehensive documentation for clang c++ compiler/linker options. The closest I could get was <a href="https://clang.llvm.org/docs/ClangCommandLineReference.html" rel="noreferrer">this page</a>, however:</p>
  <ol>
  <li>Many options aren't explained, e.g. <code>-arch</code>, <code>-arch_errors_fatal</code>, <code>-sub_umbrella</code> and many more.</li>
  <li>There are options in the Xcode command line that are missing in this doc, e.g. <code>-Wno-four-char-constants</code>, <code>-Wshorten-64-to-32</code> etc.</li>
  </ol>
  <p>Is there any place where I could find a full documentation with generous explanations for each option? Please note, I don't need the meaning of the options I gave here as examples, only for a comprehensive reference.</p>