[vala/0.40] vala: VoidType is actually compatible with itself

[Rico Tzschichholz <ricotz src gnome org>]

commit d03b0f15239d5cd5246e427eecbf1a64df5737a6
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Mon Nov 18 13:02:28 2019 +0100

    vala: VoidType is actually compatible with itself
    
    See https://gitlab.gnome.org/GNOME/vala/issues/878

 vala/valavoidtype.vala | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/vala/valavoidtype.vala b/vala/valavoidtype.vala
index 9035c25c8..1cb6f2ea4 100644
--- a/vala/valavoidtype.vala
+++ b/vala/valavoidtype.vala
@@ -34,6 +34,10 @@ public class Vala.VoidType : DataType {
                return (type2 is VoidType);
        }
 
+       public override bool compatible (DataType type2) {
+               return (type2 is VoidType);
+       }
+
        public override string to_qualified_string (Scope? scope) {
                return "void";
        }