Remove -fshort-double (PR60410)

[Jeff Law]

On 02/05/2016 12:31 PM, Bernd Schmidt wrote:
> This patch fixes PR60410 by removing -fshort-double. Nick earlier
> propsed a fix for the crash, but Richard B suggested removing the option
> entirely, and I'd agree with that. It's a pointless ABI-changing option
> on most targets, and if a port really needs it, it should be a -m option
> that tweaks DOUBLE_TYPE_SIZE.
>
> It turns out that there is still a mips config that enables it for a set
> of multilibs. As mentioned here:
>    https://gcc.gnu.org/ml/gcc-patches/2016-01/msg02140.html
> I've not managed to make that config build, it fails configuring libgcc.
> A mips maintainer would have to speak up as to whether that config is
> useful at all or not.
>
> In any case, the patch below was bootstrapped and tested on
> x86_64-linux. Ok?
Shouldn't c-opt.def be changed to note the option is deprecated and 
ignored rather than totally removing it?

OK with that change.

Jeff