C++: Fix compilation with C++<11

and MSVC that disallows override on dtor

Change-Id: I8a8897fe1318dee0c6d9b4d5d9d515e4631f9318
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>
Remove override from src/libs/3rdparty/cplusplus.

Breaks compilation with gcc 4.6 on Kubuntu 12.04 LTS as C++ 11
is not enabled.

Change-Id: Id9ddb4721775f139e82fd96c229dad481bf7647b
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Merge remote-tracking branch 'origin/3.1'