Use math_narrow_eval more consistently [committed]

[Joseph Myers]

On Thu, 24 Sep 2015, Steve Ellcey wrote:

> This patch is causing a build failure on mips16 hard-float builds.  It
> dies with:

I don't see why this would have anything to do with my patch (it's 
including math_private.h in more places, but the same set-but-not-used 
condition ought to apply to all of them), but your patch seems right for 
this case (a variable that is deliberately set but not used).

-- 
Joseph S. Myers
joseph@codesourcery.com