Refactor: `… << "\n" << std::flush;` → `… << std::endl;`

Source/cmakemain.cxx

@@ -173,11 +173,11 @@ void cmakemainMessageCallback(const std::string& m,
   // cannot use it to print messages.  Another implementation will
   // be needed to print colored messages on Windows.
   static_cast<void>(md);
-  std::cerr << m << cmakemainGetStack(cm) << '\n' << std::flush;
+  std::cerr << m << cmakemainGetStack(cm) << std::endl;
 #else
   cmsysTerminal_cfprintf(md.desiredColor, stderr, "%s", m.c_str());
   fflush(stderr); // stderr is buffered in some cases.
-  std::cerr << cmakemainGetStack(cm) << '\n' << std::flush;
+  std::cerr << cmakemainGetStack(cm) << std::endl;
 #endif
 }