In Leap 42.3, one can install gcc 5.3 from official repo.   
   Then one uses gcc-5 or g++-5 in makefiles. Invoking gcc will give you the   
   default   
   4.8.5 version. Is each version of g++ looking in the correct subdirectory to   
   pickup header files? They are in something like   
   /usr/include/c++/$version   
   There are also a few libraries in:   
   /usr/lib/gcc/$distro/$version   
   There are some guides on the web, but mostly tell you how to compile   
   another gcc from source, or else use update-alternatives thing for   
   Debian family.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)