Check for link_addr more thoroughly
Check for link_addr more thoroughly

Some versions of kFreeBSD (like 9.0) declare link_addr in a header
but lack an implementation. This makes ./configure pass but breaks
compilation later with a

     undefined reference to `link_addr'

Althought that's a bug in the OS header we can detect it easily by also
trying to link.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=715320

fabianfreyer/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,libvirt/libvirt,andreabolognani/libvirt,zhlcindy/libvirt-1.1.4-maintain,taget/libvirt,zhlcindy/libvirt-1.1.4-maintain,jfehlig/libvirt,libvirt/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,shugaoye/libvirt,jardasgit/libvirt,olafhering/libvirt,VenkatDatta/libvirt,eskultety/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,elmarco/libvirt,crobinso/libvirt,zippy2/libvirt,eskultety/libvirt,cbosdo/libvirt,taget/libvirt,datto/libvirt,agx/libvirt,elmarco/libvirt,taget/libvirt,jardasgit/libvirt,andreabolognani/libvirt,zhlcindy/libvirt-1.1.4-maintain,rlaager/libvirt,rlaager/libvirt,rlaager/libvirt,cbosdo/libvirt,datto/libvirt,zippy2/libvirt,libvirt/libvirt,andreabolognani/libvirt,agx/libvirt,agx/libvirt,zippy2/libvirt,eskultety/libvirt,agx/libvirt,crobinso/libvirt,shugaoye/libvirt,datto/libvirt,crobinso/libvirt,jardasgit/libvirt,agx/libvirt,jfehlig/libvirt,zhlcindy/libvirt-1.1.4-maintain,datto/libvirt,shugaoye/libvirt,fabianfreyer/libvirt,elmarco/libvirt,elmarco/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,olafhering/libvirt,cbosdo/libvirt,cbosdo/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,jardasgit/libvirt,eskultety/libvirt,zippy2/libvirt,taget/libvirt,taget/libvirt,zhlcindy/libvirt-1.1.4-maintain,datto/libvirt,rlaager/libvirt,nertpinx/libvirt,eskultety/libvirt,crobinso/libvirt,libvirt/libvirt,elmarco/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,nertpinx/libvirt,cbosdo/libvirt,rlaager/libvirt,olafhering/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,nertpinx/libvirt