i386 and x86_64 fenv support

[Joseph Myers]

On Tue, 27 Aug 2019, Joel Sherrill wrote:

> FWIW this moved up in importance because the x86_64 RTEMS toolchain
> won't build with the gcc/newlib master because libquadmath assumes the
> existence of the FE_TONEAREST since it the autoconf probe now sees
> we have fenv.h support now. This is probably a bug in this code since it
> can't assume a rounding mode is supported.

The rule in glibc is that architectures without support for rounding modes 
still define FE_TONEAREST, and return it from fegetround and accept it for 
fesetround, reflecting that to-nearest is the default (and only) rounding 
mode.

That is, only architectures that don't support to-nearest at all should 
fail to define FE_TONEAREST (and libquadmath doesn't support any such 
architectures anyway).

-- 
Joseph S. Myers
joseph@codesourcery.com