Compilation fix in wchar_t build after r76171.

Don't concatenate narrow wxLongLongFmtSpec with wide strings, just don't use
wxT() at all.

Closes #14685.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76172 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add wxOVERRIDE and use it in common and wxOSX code.

Make overriding virtual methods more explicit and enable additional checks
provided by C++11 compilers when "override" is used.

Closes #16100.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76173 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775