[K/N][optmz] Fixed bug with losing a part of the call graph

The bug might have happened on a failed to have been devirtualized
callsite as some of the potential callees might have been lost.
The commit solves the issue rather conservatively by simply adding
all those potential callees to the root set.

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/optimizations/CallGraphBuilder.kt

@@ -193,6 +193,12 @@ internal class CallGraphBuilder(
                     else {
                         val callSite = CallGraphNode.CallSite(call, true, call.callee)
                         callGraph.addEdge(symbol, callSite)
+
+                        allPossibleCallees.forEach {
+                            val callee = moduleDFG.functions[it]
+                            if (callee != null)
+                                functionStack.push(HandleFunctionParams(null, callee))
+                        }
                     }
                 }
             }