use UTF8-encoded char* strings in UTF8 build instead of wchar_t* if the current local...

use UTF8-encoded char* strings in UTF8 build instead of wchar_t* if the current locale uses UTF8;
fall back to widechar CRT functions in the locale is not UTF8

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45663 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775