[patch/rfc] Add host's floatformat

[DJ Delorie]

> This patch adds the host's floatformat (when known) to floatformat.[hc]. 

Since we *are* the host, don't we *always* know what the host't float
format is?  I mean, we can just cast to float.  But still, we should
be able to auto-detect which floatformat is used at runtime, rather
than guess in configure (and miss lots of host processors).

We should be able to have a pre-compiled table of float constants and
their hex representations, and just scan the table for bit equality to
see which entries match.

It might be a bit more complex to code the first time around, but it
will be a lot less hackish in the long run (and maintenance-free :)