Add wxUSE_ARTPROVIDER_STD build option.

Make it possible to exclude wxDefaultArtProvider from build. Now that a
Tango-based provider exists, it may make sense to disable the standard bitmaps
if the program doesn't need the few of them not provided by Tango anyhow.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66506 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/artprov.h

@@ -201,8 +201,10 @@ public:
 
 protected:
     friend class wxArtProviderModule;
+#if wxUSE_ARTPROVIDER_STD
     // Initializes default provider
     static void InitStdProvider();
+#endif // wxUSE_ARTPROVIDER_STD
     // Initializes Tango-based icon provider
 #if wxUSE_ARTPROVIDER_TANGO
     static void InitTangoProvider();