[O] C++ code block not linked

[Roger Mason]

Hello,

This code compiles fine on command line but org-babel can't link it.

#+BEGIN_SRC C++ :flags "-std=c++11 -I/usr/local/include" :libs  
"-L/usr/local/lib -lginac"
#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;

int main () {
    symbol a("a"), b("b"), x("x"), y("y");
    lst eqns, vars;
    eqns = a*x+b*y==3, x-y==b;
    vars = x, y;
    cout << lsolve(eqns, vars) << endl;
     // -> {x==(3+b^2)/(b+a),y==(3-b*a)/(b+a)

return 0;
}
#+END_SRC

The error buffer contains many lines like this:

/tmp//ccv5YYn1.o: In function `main':
C-src-1046xti.cpp:(.text+0x67): undefined reference to 
`GiNaC::symbol::symbol(std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> > const&)'


Org mode version 9.0.3 (release_9.0.3-170-gfed1cf @
/home/rmason/.emacs.d/org-git/org-mode/lisp/)

GNU Emacs 25.3.1 (i386-portbld-freebsd10.3, GTK+ Version 3.22.15) of
2017-11-22

Thanks for any help.

Roger