Add new definitions required by MinGW for webview. Re-enable custom schemes as a result.

See #13509

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69292 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/webview_ie.h

@@ -161,8 +161,6 @@ private:
     wxDECLARE_DYNAMIC_CLASS(wxWebViewIE);
 };
 
-#ifndef __MINGW32__
-
 class VirtualProtocol : public IInternetProtocol
 {
 protected:
@@ -227,8 +225,6 @@ private:
     wxSharedPtr<wxWebViewHandler> m_handler;
 };
 
-#endif // __MINGW32__
-
 #endif // wxUSE_WEBVIEW && wxUSE_WEBVIEW_IE && defined(__WXMSW__)
 
 #endif // wxWebViewIE_H