title: Portability of #warning preprocessor directive
body: <p>I know that the #warning directive is not standard <strong>C</strong>/C++, but several compilers support it, including gcc/g++.  But for those that don't support it, will they silently ignore it or will it result in a compile failure?  In other words, can I safely use it in my project without breaking the build for compilers that don't support it?</p>