Use string sort order with CompareString() in wxString::CmpNoCase().

Use string sort order with CompareString() in wxString::CmpNoCase().

Using the default word sort order may fail to define a strict weak order using
this function, thus breaking algorithms such as std::sort which rely on its
properties. It's also more consistent with the fallback manual implementation.

Closes #10375.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63941 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775