py27-greenlet: error: overloaded 'operator<<' must have at least one parameter of class or enumeration type

[ryandesign (Ryan Carsten Schmidt)]

py27-greenlet fails to build on El Capitan and earlier:

In file included from src/greenlet/greenlet.cpp:19:
In file included from src/greenlet/greenlet_internal.hpp:20:
src/greenlet/greenlet_greenlet.hpp:635:16: error: overloaded 'operator<<' must have at least one parameter of class or enumeration type
void greenlet::operator<<(const PyThreadState *const lhs, T& rhs)
               ^
src/greenlet/greenlet.cpp:1500:31: note: in instantiation of function template specialization 'greenlet::operator<<<_ts *>' requested here
        current->python_state << tstate;
                              ^
1 error generated.

[ryandesign (Ryan Carsten Schmidt)]

This still happens.