Simplify GTK+ 2 version checks with a helper function

Use wx_is_at_least_gtk2(minor) instead of gtk_check_version(2, minor)
because it is more clear and also works as expected (i.e. returns true)
when using GTK+ 3 instead of creating difficult to notice bugs in the
code by failing the version check in this case.

See #18004.

src/gtk/control.cpp

@@ -123,7 +123,7 @@ void wxControl::PostCreation(const wxSize& size)
 void wxControl::GTKFixSensitivity(bool WXUNUSED_IN_GTK3(onlyIfUnderMouse))
 {
 #ifndef __WXGTK3__
-    if (gtk_check_version(2,14,0)
+    if (!wx_is_at_least_gtk2(14)
 #if wxUSE_SYSTEM_OPTIONS
         && (wxSystemOptions::GetOptionInt(wxT("gtk.control.disable-sensitivity-fix")) != 1)
 #endif
@@ -348,7 +348,7 @@ wxPoint wxControl::GTKGetEntryMargins(GtkEntry* entry) const
 #if GTK_CHECK_VERSION(2,10,0)
     // The margins we have previously set
     const GtkBorder* border = NULL;
-    if (gtk_check_version(2,10,0) == NULL)
+    if (wx_is_at_least_gtk2(10))
         border = gtk_entry_get_inner_border(entry);
 
     if ( border )