Issue 3822 - Fix strict-mode in generated modules

scripts/abprewrite.js

 // This script rewrites AST to be compatible with JavaScript 1.5 and decompiles
 // the modified tree then
 
 include("../scripts/astDecompile.js");
 include("../utils/beautify.js");
 
 let headerPrinted = false;
 
 // See https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API for
 // AST structure.
@@ skipping 540 matching lines @@
   {
     // Wrap the entire module into a function to give it an independent scope.
     // Return exported symbols:
     //
     // require.scopes["foobar"] = (function() {
     //   var exports = {};
     //   ...
     //   return exports;
     // })();
     let code = 'require.scopes["' + options.filename + '"] = (function() {\n' +
-               'var exports = {};\n' +
-               decompileAST(ast) +
+               decompileAST(ast).replace(/^("use strict";\n)?/,
+                                         "$1var exports = {};\n") +
                'return exports;\n' +
                '})();\n';
     _print(js_beautify(code, options));
   }
   else
     _print(js_beautify(decompileAST(ast), options));
 }