Ada front-end depends on signed overflow

[Robert Dewar]

Eric Botcazou wrote:
>>For Ada, I propose we make the following changes:
>>   - by default, enable overflow checks using -ftrapv
> 
> 
> -ftrapv is not practically usable because (1) it generates awful code and (2) 
> it badly interacts with the RTL optimizers.
> 

please before you say this compare it with the truly awful front end
code we generate, which for sure inteferes badly with the optimizers.