A64/translate: Allow for unpredictable behaviour to be defined

include/dynarmic/A64/config.h

@@ -158,6 +158,11 @@ struct UserConfig {
     /// This is only used if page_table is not nullptr.
     bool silently_mirror_page_table = true;
 
+    /// This option relates to translation. Generally when we run into an unpredictable
+    /// instruction the ExceptionRaised callback is called. If this is true, we define
+    /// definite behaviour for some unpredictable instructions.
+    bool define_unpredictable_behaviour = false;
+
     // The below options relate to accuracy of floating-point emulation.
 
     /// Determines how accurate NaN handling is.