core: allow product to provide kernel headers as well

This is useful when a device inherits from an architecture
product, such as omap4.mk. The architecture specific product
can provide kernel headers to all the devices that use
that architecture.

Change-Id: I0c9d3120a6089fb535a3fa8eccf10775a271cd21
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/core/product_config.mk b/core/product_config.mk
index c455723..ea3e517 100644
--- a/core/product_config.mk
+++ b/core/product_config.mk
@@ -306,6 +306,10 @@
 # An list of whitespace-separated words.
 PRODUCT_TAGS := $(strip $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_TAGS))
 
+# The list of product-specific kernel header dirs
+PRODUCT_VENDOR_KERNEL_HEADERS := \
+    $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VENDOR_KERNEL_HEADERS)
+
 # Add the product-defined properties to the build properties.
 ADDITIONAL_BUILD_PROPERTIES := \
     $(ADDITIONAL_BUILD_PROPERTIES) \