[cairo] Flag for FP-challenged platforms

[Daniel Amelang]

I've recently developed some optimizations in cairo that speed up
platforms w/out an FPU, but slow down those that do. Carl has also
mentioned being in this situation, and so I'm proposing a new
configure option and flag. How do you all feel about the following
proposed names?

--avoid-floating-point and AVOID_FLOATING_POINT
--avoid-floats and AVOID_FLOATS
--avoid-float and AVOID_FLOAT
--avoid-float-operations and AVOID_FLOAT_OPERATIONS

I'm shying away from --enable-embedded or the like, as I'd prefer the
flag to describe the effect that it has on the code produced instead
of describing the context where it is expected to be used.

Also, it would be nice to be able to guess this value for a given
arch, but that's a little tricky. Like ARM with VFP would actually
want to use FP, while ARM w/out VFP would not. I've seen people do
this:

#if defined(__arm__) && !defined(__VFP__)

which I think would cover the one and only situation that we know of
where cairo should avoid FP operations. Thoughts?

Dan