MSVC: Enable standards-conforming mode

Let's not allow any new code that uses non-conforming syntaxes. With
GCC and like, we already use -std=c++11 instead of -std=gnu++11 for that
very reason.

Change-Id: I4a7dc1fe14154695b968fffd14aba9f8cea69c47
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>