[Development] Removing the -c++11 option from configure

[Stephen Kelly]

Thiago Macieira wrote:

> The reason we prefer -std=c++11 is that it allows us to write code that
> doesn't trip GNU extensions unlikely to be found on MSVC and other
> compilers. 

What is the likelyhood of that? No one is going to accidentally add an 
`__attribute ((strong))` namespace in Qt. 

In particular, what features are you afraid of accidentally using (locally 
on your machine before CI gets a look) which are available with -std=gnu++11 
but not available with -std=c++11?

> So I really want to keep -std=c++11, except for a module or two
> that really need it (QtBluetooth comes to mind due to BlueZ headers
> assuming GCC extensions are enabled).

Yes, changing the default mode of the compiler ('enable extensions') is bad 
for dependencies. Dependency code ifdefs on __STRICT_ANSI__.

> User code has been using this flag just fine for a couple of years, so I
> don't think they need -std=gnu++11.

Yes. I did see a lot of issues pop up around mingw, but as you say, Qt 
people haven't noticed anything. Is that really a good reason not to fix it? 
Unreported bugs are fixed all the time.

Anyway, now you know the problem, you can do what you think is best.

Thanks,

Steve.