Fix build on macos

[eilvelia]

• The SgProcess object file is empty in case clang is used, however ranlib on macos does not allow those (it fails with the ... has no symbols error)
• There was the following error because of using boost::thread and using namespace std simultaneously:

  benzene-vanilla-cmake/src/gtpengine/GtpEngine.cpp:357:9: error: reference to 'thread' is ambiguous
      thread::sleep(time);

• I also fixed this:

  benzene-vanilla-cmake/src/solver/SolverDB.hpp:135:5: error: void function 'SetParameters' should not return a value [-Wreturn-type]
  return m_param = p;