Fix: make sure function name doesn't collide with argument names

Usually the function name is dropped if the function is a function expression. But when `ie8` option is enabled, the function name is kept and mangled which may break legacy Safari for said reason. Since symbol names are now [mangled from within](https://github.com/mishoo/UglifyJS2/pull/2948#issuecomment-368095376), this fix adds argument names to existing names when mangling the name of a function expression.

lib/scope.js

@@ -320,6 +320,15 @@ function next_mangled_name(scope, options, def) {
     var in_use = names_in_use(scope, options);
     var holes = scope.cname_holes;
     var names = Object.create(null);
+    // #179, #326
+    // in Safari strict mode, something like (function x(x){...}) is a syntax error;
+    // a function expression's argument cannot shadow the function expression's name
+    if (options.ie8 && (def.init instanceof AST_Function && def.init.argnames.length > 0)) {
+        for (var i = 0, len = def.init.argnames.length; i < len; i++) {
+            var arg = def.init.argnames[i];
+            names[arg.definition().mangled_name] = true;
+        }
+    }
     var scopes = [ scope ];
     def.references.forEach(function(sym) {
         var scope = sym.scope;

test/mocha/safari9.js

@@ -0,0 +1,26 @@
+var assert = require('assert');
+var UglifyJS = require('../..');
+
+describe('legacy safari', function() {
+    it('Should make sure mangled function name is different from its argument names', function () {
+        assert.strictEqual(
+            UglifyJS.minify([
+                'function main() {',
+                '    "use strict";',
+                '    ',
+                '    function n(a,b,c) {',
+                '        console.log(c)',
+                '    }',
+                '    E.on = function f2() {',
+                '        E.on(function(e) {',
+                '            return n(this,e)',
+                '        })',
+                '    }',
+                '}'
+            ].join('\n'), {
+                ie8: true
+            }).code,
+            'function main(){"use strict";E.on=function(){E.on(function(n){return function c(n,o,t){console.log(t)}()})}}'
+        )
+    })
+})