libdispatch on 8-Stable or 9-Current

[Ollivier Robert]

According to Tom Pusateri:
> and rebuilt the world but kern.osreldate didn't change. Its still 800107 which won't allow the port to build.

Change the <= into a < in libdispatch/Makefile and it will happily build the port.
All tests pass.

I'm using a fairly recent clang snapshot for the blocks support.

llvm-devel-2.7.r89141       (made with "make BOOTSTRAP=yes makesum && update)
libdispatch-147
compiler-rt-0.r83568

FreeBSD ng.keltia.net 8.0-PRERELEASE FreeBSD #6 r199493M: Wed Nov 18 22:33:04 CET 2009