Use of DI mode on 32-bit hosts

[Doug Evans]

Ben Elliston writes:
 > I believe configuring from the top-level was removed because it was
 > thought that cgen didn't need configuring -- it runs entirely from the
 > source tree, via Makefile targets in other build directories, like
 > opcodes.
 > 
 > It was concluded that this is incorrect, though, because it is needed
 > to build the documentation at the very least.  I don't know if the
 > top-level gear was put back or not.

Not to mention the loss of Hobbit support.  Boo hoo hoo ....