Build failure with libc++ 3.9.0

In file included from /wrkdirs/usr/ports/devel/qbs/work/qbs-src-1.6.1/src/lib/corelib/api/internaljobs.cpp:39:
In file included from /wrkdirs/usr/ports/devel/qbs/work/qbs-src-1.6.1/src/lib/corelib/buildgraph/executor.h:45:
/usr/include/c++/v1/queue:400:5: error: static_assert failed ""
    static_assert((is_same<_Tp, value_type>::value), "" );
    ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/wrkdirs/usr/ports/devel/qbs/work/qbs-src-1.6.1/src/lib/corelib/buildgraph/executor.h:156:12: note: in instantiation of template class
      'std::__1::priority_queue<qbs::Internal::Artifact *, std::__1::vector<qbs::Internal::BuildGraphNode *,
      std::__1::allocator<qbs::Internal::BuildGraphNode *> >, qbs::Internal::Executor::ComparePriority>' requested here
    Leaves m_leaves;
           ^