On Windows, don't try to create relative paths across different drives

pylib/gyp/common.py

Index: pylib/gyp/common.py
===================================================================
--- pylib/gyp/common.py	(revision 1672)
+++ pylib/gyp/common.py	(working copy)
@@ -131,6 +131,13 @@
   path = os.path.realpath(path)
   relative_to = os.path.realpath(relative_to)
 
+  # On Windows, we can't create a relative path to a different drive, so just
+  # use the absolute path.
+  if os.name == 'nt':

[scottmg, 2013/07/19 16:51:17]

i'm not sure whether this will work on cygwin... isn't there some /cygdrive/
crud it uses instead? does splitdrive work on that? so maybe sys.platform ==
'win32' makes more sense. (other places use sys.platform, so if you think it
works on cygwin, then sys.platform in ('win32', 'cygwin') for consistency)

[borenet, 2013/07/19 17:58:42]

Changed to use sys.platform == "win32".  I just verified that this isn't
necessary on cygwin, since relative paths do work between drives, because of the
/cygdrive prefix and Unix-style paths.

+    if (os.path.splitdrive(path)[0].lower() !=
+        os.path.splitdrive(relative_to)[0].lower()):
+      return path
+
   # Split the paths into components.
   path_split = path.split(os.path.sep)
   relative_to_split = relative_to.split(os.path.sep)