Add wxHAS_LONG_LONG_T_DIFFERENT_FROM_LONG symbol.

Add wxHAS_LONG_LONG_T_DIFFERENT_FROM_LONG symbol.

Instead of writing a rather unreadable "defined(wxLongLong_t) &&
!defined(wxLongLongIsLong)" expression every time we need to decide if a
function needs to be overloaded for both long and long long, add a new symbol
which can be tested directly.

No real changes in the code.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66711 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775