message: Fix include in test_document.cpp when building against libc++
diff: # include <stdexcept>
  #endif
  -#ifdef __MINGW32__
  -# include <io.h> // for unlink in C++0x mode
  -#endif
  -
  -#if defined(__CELLOS_LV2__) || defined(ANDROID) || defined(_GLIBCXX_HAVE_UNISTD_H) || defined(__APPLE__)
  -# include <unistd.h> // for unlink
  +// for unlink
  +#ifdef _WIN32
  +# include <io.h>
  +#else
  +# include <unistd.h>
  #endif
  using namespace pugi;
  