Merge the new gdtoa: Note that the built-in tests fail the same way as with
the old gdtoa.

* Pacify compiler; delint.
* Add MI NetBSD definitions.
* Rename IEEE_{8087,MC68k} to IEEE_{LITTLE,BIG}_ENDIAN, as previously
done in strtod.c.
* Some const poisoning, more to follow.

Import gdtoa-2005-09-23; test suite will be imported separately.