RFA: Add dummy fenv.h to libc/include

[Nick Clifton]

Hi Corinna,

> After reading the description of the fenv.h header in SUSv3, I think
> that providing the header w/o actually providing the functionality
> is also a violation of the standard.  The spec for fenv.h contains
> wording like:
> 
>   "The <fenv.h> header shall define the following constants if and only
>   if the implementation supports the floating-point exception by means
>   of the floating-point functions [...]"

> The bottom line is, wouldn't it be better to add the dummy header only
> to the testsuite which needs this file to run specific tests, rather
> than creating a dummy file which affects all newlib targets and might
> result in spurious run-time failures?

*sigh*  Yes you are right.  The header does violate the ISO C99 standard.  Oh 
well.  I withdraw this patch and I will have to think about what we can do to 
actually implement the functionality for real.

Cheers
   Nick