Fix PR rtl-optimization/42461

[Eric Botcazou]

> I guess something like
> float
> __attribute__ ((noinline,noclobber))
> const_function (float a, float b)
> {
>   return a/b;
> }
> main()
> {
>   const_function (1,0);
> }
>
> with non-call exceptions.  It does throw but DCE should remove it with this
> change I believe.

And we didn't before the EH rewrite?

> We still need to retain here some what to differentiate nothrow and normal
> calls...

I don't think this was ever done for RTL DCE though, only for Tree DCE.

-- 
Eric Botcazou