reverted from https://hg.mozilla.org/mozilla-central/rev/aa63a2a40325
--- dom/bindings/GenerateCSS2PropertiesWebIDL.py.orig
+++ dom/bindings/GenerateCSS2PropertiesWebIDL.py
@@ -16,7 +16,7 @@
     return "  [%s] attribute DOMString %s;\n" % (", ".join(extendedAttrs),
                                                  propName)
 def generate(output, idlFilename, preprocessorHeader):
-    cpp = list(buildconfig.substs['CPP'])
+    cpp = shellutil.split(buildconfig.substs['CPP'])
     cpp += shellutil.split(buildconfig.substs['ACDEFINES'])
     cpp.append(preprocessorHeader)
     preprocessed = subprocess.check_output(cpp)
--- layout/style/GenerateCSSPropsGenerated.py.orig
+++ layout/style/GenerateCSSPropsGenerated.py
@@ -10,7 +10,7 @@
 from mozbuild import shellutil
 
 def get_properties(preprocessorHeader):
-    cpp = list(buildconfig.substs['CPP'])
+    cpp = shellutil.split(buildconfig.substs['CPP'])
     cpp += shellutil.split(buildconfig.substs['ACDEFINES'])
     cpp.append(preprocessorHeader)
     preprocessed = subprocess.check_output(cpp)
