The build fails with error: call of overloaded ‘swap(boost::blank&, boost::blank&)’ is ambiguous swap(lhs, rhs); Confirmed on the icinga2 bug tracker (see URL).
Glad to see that this is why it was failing to build
I do think that this only impacted 2.6.0.
Upstream acked that this is a known issue in boost, either use an old version or a new version, the current stable has a known bug.