title: How do you write a makefile for both clang and gcc?
body: <p>I would like to use <code>std::experimental::filesystem</code> in my code, this requires me to compile using <code>-lstdc++fs</code> with GCC and <code>-lc++experimental</code> with Clang. At the moment I have a <code>makefile</code> and <code>makefile.clang</code> reflecting the difference in compilation, alternatively I've thought about using a clang build target so I can run <code>build clang</code>.</p>
  
  <p>Is there some canonical way to set compiler-specific flags in a makefile?</p>