Fix compilation with -std=gnu++11

[tfry-git]

See #402

[lacklustrlabs]

I wonder if we really need the #if __cplusplus >= 201103L tests.
http://www.stm32duino.com/viewtopic.php?f=3&t=1241&p=38520#p38520

C++17 has already been approved, so why struggle with C++03 or earlier versions?

[tfry-git]

I suppose it depends which compilers we may still want to support. If we are all set to stick with C++11(or later) for good, a fix without standards version check is even more trivial. I don't mind if this request is rejected, I'd just like to get the issue fixed one way or another.

[stevstrong]

gnu11 was introduced without any fallback scenario.
So we don't need any ifdefs.

[tfry-git]

Next attempt: #407

(Seems I can change the target branch to merge to, but not the source branch to merge form in a PR)