xcode_settings entries with list values override entries with the same key

pylib/gyp/xcodeproj_file.py

Index: pylib/gyp/xcodeproj_file.py
===================================================================
--- pylib/gyp/xcodeproj_file.py	(revision 1556)
+++ pylib/gyp/xcodeproj_file.py	(working copy)
@@ -1556,13 +1556,13 @@
     return self._properties['buildSettings'][key]
 
   def SetBuildSetting(self, key, value):
-    # TODO(mark): If a list, copy?
-    self._properties['buildSettings'][key] = value
+    if hasattr(value, '__iter__'):
+      self._properties['buildSettings'].setdefault(key, []).extend(value)
+    else:
+      self._properties['buildSettings'][key] = value
 
   def AppendBuildSetting(self, key, value):
-    if not key in self._properties['buildSettings']:
-      self._properties['buildSettings'][key] = []
-    self._properties['buildSettings'][key].append(value)
+    self._properties['buildSettings'].setdefault(key, []).append(value)
 
   def DelBuildSetting(self, key):
     if key in self._properties['buildSettings']: