Include vendor overrides in system prop if not split

Bug: 163854285
Test: m on crosshatch. Vendor overrides are included in
system/build.prop on legacy devices.

Change-Id: Ib134f934de8546af3dff27312f6877eafe5ed22c
diff --git a/core/sysprop.mk b/core/sysprop.mk
index d01255f..73dbec7 100644
--- a/core/sysprop.mk
+++ b/core/sysprop.mk
@@ -300,7 +300,8 @@
 
 ifndef property_overrides_split_enabled
 _prop_vars_ += \
-    ADDITIONAL_VENDOR_PROPERTIES
+    ADDITIONAL_VENDOR_PROPERTIES \
+    PRODUCT_VENDOR_PROPERTIES
 endif
 
 _blacklist_names_ := \