fenv.h fixes for softfloat

[David Schultz]

On Wed, Jan 11, 2012, Ian Lepore wrote:
> I can probably find time to work with it a bit more, I just wanted to
> quickly post the initial results, especially in case the feedback was
> along the lines of "thanks, but testing in an 8.2 environment won't
> work."  We rely pretty heavily on floating point math on ARM at work, so
> I may even be able to dedicate some non-hobbyist cycles to it (it occurs
> to me that running the whole suite of regression tests now that we've
> upgraded from 6.2->8.2 would probably be wise).

That would be great.  A few of the libm regression tests and libm
functions depend on fenv.h working, by the way.  But most of the
important stuff should work.