rfc: replacing fp-bit with glibc's soft-fp implementation

[Aldy Hernandez <aldyh at redhat dot com>]

I've talked with this over with Geoff and Richard on and off over the 
past few months, and I've finally decided to give it a go.  Before I 
sink any time into it, I'd like to get people's input, to make sure 
there are no objections.

Glibc's soft-fp/ implementation (also used in the Linux kernel) is both 
faster, and more accurate.  Not to mention, it also provides exceptions 
and rounding modes.

If done right in both glibc and gcc, we can even provide a completely 
soft float implementation that is IEEE/ISO compliant for systems that 
have no hardware floating point.  We would of course have to define an 
interface between libgcc and glibc to set rounding modes and exceptions.

There is a thread about this on the glibc list a while back, when I was 
writing a completely soft float implementation for PPC glibc.  The 
interesting bits are here:

	http://sources.redhat.com/ml/libc-alpha/2002-11/msg00044.html

I was thinking we could migrate back ends one at a time to the soft-fp/ 
implementation, and remove the fp-bit stuff once all the back ends are 
migrated.  The reason I mention this is because of the _FP_DIV*, _FP_* 
macros that each back end will need to provide.

Anywhoo, the details are a bit sketchy, but I wanted to bring this up, 
to see what everyone else thought.

Thoughts?

Aldy