Log Message:
lang/gcc46: Mark NOT-FOR-DRAGONFLY

A very large number of patches is required to properly build a stock
gcc on DragonFly, as evidenced by the patches added to lang/gcc47.
DragonFly already has a very good gcc46-based compiler in lang/gnat-aux.
DragonFly users that specifically need gcc46 have been told to use
gnat-aux.  There's no need to make maintenance of lang/gcc46 harder so
it's masked on DragonFly to show its intentionally unsupported.