Fix ABI on dragonfly

Define dragonfly as legitimate value for elf notes and also updates the ABI
version which is different than FreeBSD. FreeBSD only needs whole numbers for
the version (e.g. 8,9,10) while DragonFly needs evenly numbered point versions
(e.g. 3.4, 3.6, 3.8).

The development branches are oddly numbered (e.g. 3.3, 3.5) but packages created
by these branches should be valid for the upcoming release, so 3.3 will round to
3.4 for the ABI version.