Clean up the libunbound build to avoid accidentally regenerating the
configuration lexer and parser during buildworld.  Instead of being
included in the source as it is in the upstream distribution, the code is
now always generated (in ${.OBJDIR}) at build time.

PR:		190739
MFC after:	1 week
Check if the specified group is the user's primary group before
iterating over the (possibly empty) list of members.  Otherwise, we
get a false negative when the target group has no members listed in
/etc/group.  This went mostly unnoticed because root is explicitly
listed as a member of wheel, so the bug is never triggered in the most
common use case, which is su(8).

PR:		109416
MFC after:	1 week
Handle nested exceptions in bhyve.

A nested exception condition arises when a second exception is triggered while
delivering the first exception. Most nested exceptions can be handled serially
but some are converted into a double fault. If an exception is generated during
delivery of a double fault then the virtual machine shuts down as a result of
a triple fault.

vm_exit_intinfo() is used to record that a VM-exit happened while an event was
being delivered through the IDT. If an exception is triggered while handling
the VM-exit it will be treated like a nested exception.

vm_entry_intinfo() is used by processor-specific code to get the event to be
injected into the guest on the next VM-entry. This function is responsible for
deciding the disposition of nested exceptions.