fix corner case in dead_code (#5107)

fixes #5106

lib/compress.js

@@ -11472,7 +11472,7 @@ merge(Compressor.prototype, {
                 var local = scope === compressor.find_parent(AST_Lambda);
                 var level = 0, node;
                 parent = compressor.self();
-                do {
+                if (!(scope.uses_arguments && is_funarg(def)) || compressor.has_directive("use strict")) do {
                     node = parent;
                     parent = compressor.parent(level++);
                     if (parent instanceof AST_Assign) {

test/compress/dead-code.js

@@ -1633,3 +1633,39 @@ issue_5030: {
     expect_stdout: "PASS"
     node_version: ">=0.12"
 }
+
+issue_5106_1: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        console.log(typeof function(a) {
+            return a = arguments;
+        }("FAIL")[0]);
+    }
+    expect: {
+        console.log(typeof function(a) {
+            return a = arguments;
+        }("FAIL")[0]);
+    }
+    expect_stdout: "object"
+}
+
+issue_5106_2: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        "use strict";
+        console.log(function(a) {
+            return a = arguments;
+        }("PASS")[0]);
+    }
+    expect: {
+        "use strict";
+        console.log(function(a) {
+            return arguments;
+        }("PASS")[0]);
+    }
+    expect_stdout: "PASS"
+}

test/jetstream.js

@@ -68,6 +68,7 @@ if (typeof phantom == "undefined") {
         (function install() {
             npm([
                 "install",
+                "graceful-fs@4.2.6",
                 "phantomjs-prebuilt@2.1.14",
                 "--no-audit",
                 "--no-optional",