Fix building BIND on DragonFly BSD
This commit ensures that BIND and supplementary tools still can be built on newer versions of DragonFly BSD. It used to be the case, but somewhere between versions 6.2 and 6.4 the OS developers rearranged headers and moved some function definitions around.
Before that the fact that it worked was more like a coincidence, this time we, at least, looked at the related man pages included with the OS.
No in depth testing has been done on this OS as we do not really support this platform - so it is more like a goodwill act. We can, however, use this platform for testing purposes, too. Also, we know that the OS users do use BIND, as it is included in its ports directory.
Building with './configure' and './configure --without-jemalloc' have been fixed and are known to work at the time the commit is made.
Closes #3796 (closed)