Use system command to unzip binaries from zip file on Mac OS

tools/bisect-builds.py

Index: tools/bisect-builds.py
diff --git a/tools/bisect-builds.py b/tools/bisect-builds.py
index 6d0830f8d29752c2790c4e878f3376e941b5c7f7..a87807e4d826a4662c4c5894d94b6a22ec848e07 100755
--- a/tools/bisect-builds.py
+++ b/tools/bisect-builds.py
@@ -452,16 +452,32 @@ class PathContext(object):
                                                    self.bad_revision)
     return revlist
 
+
+def IsMac():
+  return sys.platform.startswith('darwin')
+
+
 def UnzipFilenameToDir(filename, directory):
   """Unzip |filename| to |directory|."""
   cwd = os.getcwd()
   if not os.path.isabs(filename):
     filename = os.path.join(cwd, filename)
-  zf = zipfile.ZipFile(filename)
   # Make base.
   if not os.path.isdir(directory):
     os.mkdir(directory)
   os.chdir(directory)
+
+  # The Python ZipFile does not support symbolic links, which makes it
+  # unsuitable for Mac builds. so use ditto instead.
+  if IsMac():
+    unzip_cmd = ['ditto', '-x', '-k', filename, '.']
+    proc = subprocess.Popen(unzip_cmd, bufsize=0, stdout=subprocess.PIPE,
+                            stderr=subprocess.PIPE)
+    proc.communicate()
+    os.chdir(cwd)
+    return
+
+  zf = zipfile.ZipFile(filename)
   # Extract files.
   for info in zf.infolist():
     name = info.filename