Fix lastchange.py when running on native win32 python

build/util/lastchange.py

Index: build/util/lastchange.py
diff --git a/build/util/lastchange.py b/build/util/lastchange.py
index d419f92b5c866544bbda17801632204212c39d3f..a101341ef7d3e176fcebfc08e3b6f6671617be00 100755
--- a/build/util/lastchange.py
+++ b/build/util/lastchange.py
@@ -73,20 +73,18 @@ def RunGitCommand(directory, command):
     A process object or None.
   """
   command = ['git'] + command
-  shell = True
   # Force shell usage under cygwin. This is a workaround for
   # mysterious loss of cwd while invoking cygwin's git.
   # We can't just pass shell=True to Popen, as under win32 this will
   # cause CMD to be used, while we explicitly want a cygwin shell.
   if sys.platform == 'cygwin':
     command = ['sh', '-c', ' '.join(command)]
-    shell = False
   try:
     proc = subprocess.Popen(command,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE,
                             cwd=directory,
-                            shell=shell)
+                            shell=(sys.platform=='win32'))
     return proc
   except OSError:
     return None