GN: Fix library flag generation logic

third_party/cython/python_flags.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import argparse
 import os
 import sys
 
 from distutils import sysconfig
 from distutils.command import build_ext
@@ skipping 16 matching lines @@
                       action='store_true')
   opts = parser.parse_args()
 
   ext = Extension('Dummy', [])
   b = build_ext.build_ext(Distribution())
   b.initialize_options()
   b.finalize_options()
   result = []
   if opts.libraries:
     libraries = b.get_libraries(ext)
-    if sys.platform in ['darwin', 'linux2']:
-      # In case of darwin and linux prefix all libraries (if there is any)
-      # so it can be used as a compiler argument.
+    if sys.platform == 'darwin':
+      libraries.append('python%s' % sys.version[:3])
+    if not opts.gn and sys.platform in ['darwin', 'linux2']:
+      # In case of GYP output for darwin and linux prefix all
+      # libraries (if there are any) so the result can be used as a
+      # compiler argument. GN handles platform-appropriate prefixing itself.
       libraries = ['-l%s' % library for library in libraries]
-      if sys.platform == 'darwin':
-        libraries.append('-lpython%s' % sys.version[:3])
     result.extend(libraries)
   if opts.includes:
     result = result  + b.include_dirs
   if opts.library_dirs:
     if sys.platform == 'darwin':
       result.append('%s/lib' % sysconfig.get_config_vars('prefix')[0])
 
   if opts.gn:
     for x in result:
       print x
   else:
     print ''.join(['"%s"' % x for x in result])
 
 if __name__ == '__main__':
   main()