libpthread version bump

[Warner Losh]

> > The recent changes to implement the the %fs/%gs manipulation syscalls has
> > created a problem for 5.x compatibility.  While libc has been bumped for
> > 6.x already, libpthread hasn't, so running 5.x apps on -CURRENT ends up
> > with the app pulling in the old libc correctly, but it pulls in the
> > current libpthread which depends on the new libc and the linker errors out
> > on the missing symbols.
> >
> > I think we need to bump libpthread's version to allow for compatibility in
> > 6. Then we can ship the old libpthread along with the old libc and the
> > Right Thing happens.
> 
> I wish someone would work on getting symbol versioning working
> so we don't have to keep bumping library versions for things
> like this :-)

Symbol versioning wouldn't help this case...

Warner