[RFA] Enable -Wsuggest-override

[Pedro Alves]

On 04/27/2018 03:07 PM, Tom Tromey wrote:
> I noticed the existence of -Wsuggest-override and so this patch
> enables it for gdb.  It found a few spots that could use "override".
> Also I went ahead and removed all uses of the "OVERRIDE" macro.
> 
> Using override is beneficial because it makes it harder to change a
> base class and then forget to change a derived class.
> 
> Tested by the buildbot.

Yes, please.  OK.

Thanks,
Pedro Alves