Fix MacOS missing symbol __ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEElsEi.

This is triggered by emitting operator<< 'class std::__1::basic_ostream<char,
struct std::__1::char_traits<char> > &(int)' even though its marked as exported
in general. Now that clang and libc++ agree on the handling of exported
templates we can remove our work-around.