Fixing cygwin specific assumptions in gyp diff writer.

pylib/gyp/common.py

Index: pylib/gyp/common.py
===================================================================
--- pylib/gyp/common.py	(revision 379)
+++ pylib/gyp/common.py	(working copy)
@@ -5,6 +5,7 @@
 import os.path
 import re
 import tempfile
+import sys
 
 
 def BuildFileAndTarget(build_file, target):
@@ -259,6 +260,11 @@
           umask = os.umask(077)
           os.umask(umask)
           os.chmod(self.tmp_path, 0666 & ~umask)
+          if sys.platform == 'win32':
+            # NOTE: on windows (but not cygwin) rename will not replace an
+            # existing file, so it must be preceded with a remove. Sadly there
+            # is no way to make the switch atomic.
+            os.remove(filename)
           os.rename(self.tmp_path, filename)
       except Exception:
         # Don't leave turds behind.