Small fix to graph building

We don't need to walk up the supertype chain for type targets of
indirect calls, we already do that for function implementations which
would reach the type of the indirect call anyway

Author: stevenfontanella

src/passes/GlobalEffects.cpp

@@ -161,12 +161,14 @@ CallGraph buildCallGraph(const Module& module,
     if (!closedWorld) {
       continue;
     }
-
     // Function -> Type
     allFunctionTypes.insert(caller->type.getHeapType());
     for (HeapType calleeType : callerInfo.indirectCalledTypes) {
       callees.insert(calleeType);
-      allFunctionTypes.insert(calleeType);
+
+      // Add the key to ensure the lookup doesn't fail for indirect calls to
+      // uninhabited types.
+      callGraph[calleeType];
     }
 
     // Type -> Function