dont symlink if it's already correctly linked

build/symlink.py

 #!/usr/bin/env python
 # Copyright (c) 2013 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.
 
 """Make a symlink and optionally touch a file (to handle dependencies)."""
 
 
 import errno
 import optparse
@@ skipping 10 matching lines @@
   options, args = parser.parse_args(argv[1:])
   if len(args) < 2:
     parser.error('at least two arguments required.')
 
   target = args[-1]
   sources = args[:-1]
   for s in sources:
     t = os.path.join(target, os.path.basename(s))
     if len(sources) == 1 and not os.path.isdir(target):
       t = target
+    if os.path.realpath(t) == s:
+      continue
     try:
       os.symlink(s, t)
     except OSError, e:
       if e.errno == errno.EEXIST and options.force:
         if os.path.isdir(t):
           shutil.rmtree(t, ignore_errors=True)
         else:
           os.remove(t)
         os.symlink(s, t)
       else:
         raise
 
 
   if options.touch:
     with open(options.touch, 'w') as f:
       pass
 
 
 if __name__ == '__main__':
   sys.exit(Main(sys.argv))