boost-libs build failure

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

A -current/amd64, gcc 5.4.0, pbulk run fails to build boost-libs 1.65.0 with:

./boost/stacktrace/detail/collect_unwind.ipp: In function '_Unwind_Reason_Code boost::stacktrace::detail::unwind_callback(_Unwind_Context*, void*)':
./boost/stacktrace/detail/collect_unwind.ipp:34:43: error: expected id-expression before numeric constant
     return _Unwind_GetIP(context) ? ::_URC_NO_REASON : ::_URC_END_OF_STACK;
                                       ^
./boost/stacktrace/detail/collect_unwind.ipp:34:43: error: expected ':' before numeric constant                                                                           
etc


Cheers,

Patrick