Remove -fexceptions configure test

[Joseph Myers]

On Sun, 18 Oct 2015, Szabolcs Nagy wrote:

> i think -fasynchronous-unwind-tables don't need -fexceptions
> (currently).
> 
> -fasync* means unwind can propagate from anywhere, cleanups
> are not run.

So do you think cases with callbacks (which might be C++ functions 
throwing exceptions through libc code) need -fexceptions, or only 
-funwind-tables?

-- 
Joseph S. Myers
joseph@codesourcery.com