Issue 5216 - [emscripten] Use a more reliable way of retrieving mangled function name

compile

 #!/usr/bin/env python
 
 # This file is part of Adblock Plus <https://adblockplus.org/>,
 # Copyright (C) 2006-2017 Eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus is distributed in the hope that it will be useful,
@@ skipping 58 matching lines @@
         'PYTHON': scope.get('PYTHON', sys.executable),
         'NODE_JS': scope.get('NODE_JS', 'node'),
     })
     return env
 
 
 def generate_bindings(env):
     params = [
         env['PYTHON'], os.path.join(env['EMSCRIPTEN'], 'emcc'),
         '-o', BINDINGS_GENERATOR, '-std=gnu++14', '--js-library', JS_LIBRARY,
+        '--js-library', os.path.join(SOURCE_DIR, 'bindings', 'library.js'),
     ] + list(get_source_files('bindings'))
     subprocess.check_call(params, env=env)
 
     with open(BINDINGS_OUTPUT, 'w') as file:
         subprocess.check_call([env['NODE_JS'], BINDINGS_GENERATOR],
                               stdout=file)
 
 
 def run_compiler(env, debug=False, tracing=False):
     params = [
@@ skipping 33 matching lines @@
     parser.add_argument(
         '-t', '--tracing',
         action='store_true',
         help='Enable memory tracing'
     )
     args = parser.parse_args()
 
     env = getenv(args.emscripten_config)
     generate_bindings(env)
     run_compiler(env, debug=args.debug, tracing=args.tracing)