dhclient less functional with nanobsd because of NO_CXX

[Robert Watson]

Observation on dependencies between components and nanobsd:

In the old world order, dhclient backgrounded and waited for the link 
state to come up.  In the new world order, dhclient exits if the link 
state is down, relying on devd to restart it.  devd isn't build if NO_CXX 
is set, as it's written in C++, and NO_CXX is a useful (and default) thing 
to set for nanobsd for obvious reasons.  It sounds like something here is 
an argument for:

- Allowing C++ to be built as a build dependency, but not installed.
- Rewriting devd to not be in C++.
- Providing an option so that dhclient's old and useful behavior can be
   restored.

Glancing at the dhclient man page didn't suggest an obvious command line 
flag for "don't exit on no link state"...

Robert N M Watson