message: [vcpkg] Add case for exe path discovery for macos
diff: #include <time.h>
  +#if defined(__APPLE__)
  +# include <mach-o/dyld.h>
  +#endif
  +
  #pragma comment(lib, "Advapi32")
  namespace vcpkg::System
  @@ -31,7 +35,15 @@ namespace vcpkg::System
  const int bytes = GetModuleFileNameW(nullptr, buf, _MAX_PATH);
  if (bytes == 0) std::abort();
  return fs::path(buf, buf + bytes);
  -#else
  +#elif __APPLE__
  + uint32_t size = 1024 * 32;
  + char buf[size] = {};
  + bool result = _NSGetExecutablePath(buf, &size);
  + Checks::check_exit(VCPKG_LINE_INFO, result != -1, "Could not determine current executable path.");
  + std::unique_ptr<char> canonicalPath (realpath(buf, NULL));
  + Checks::check_exit(VCPKG_LINE_INFO, result != -1, "Could not determine current executable path.");
  + return fs::path(std::string(canonicalPath.get()));
  +#else /* LINUX */
  std::array<char, 1024 * 4> buf;
  auto written = readlink("/proc/self/exe", buf.data(), buf.size());
  Checks::check_exit(VCPKG_LINE_INFO, written != -1, "Could not determine current executable path.");
  