Implemented extern functions

src/compiler/Compile.go

@@ -108,6 +108,10 @@ func CompileFunctions(functions map[string]*core.Function) {
 	wg := sync.WaitGroup{}
 
 	for _, function := range functions {
+		if function.IsExtern() {
+			continue
+		}
+
 		wg.Add(1)
 
 		go func() {