Add PRODUCT_IOT to the list of product vars.

This variable tells whether the product is an Android Things variant of
Android.

Bug: 32549448
Test: `make dist` on an iot product.
Change-Id: I0875951ae57867bc8bf47885e77e494d6284acdb
diff --git a/core/product.mk b/core/product.mk
index 7d7c68b..fffd7c8 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -128,6 +128,7 @@
     VENDOR_EXCEPTION_MODULES \
     VENDOR_EXCEPTION_PATHS \
     PRODUCT_ART_USE_READ_BARRIER \
+    PRODUCT_IOT \
 
 
 
diff --git a/core/product_config.mk b/core/product_config.mk
index 8943429..dc71d5d 100644
--- a/core/product_config.mk
+++ b/core/product_config.mk
@@ -420,3 +420,7 @@
 # Make this art variable visible to soong_config.mk.
 PRODUCT_ART_USE_READ_BARRIER := \
     $(strip $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_ART_USE_READ_BARRIER))
+
+# Whether the product is an Android Things variant.
+PRODUCT_IOT := \
+    $(strip $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_IOT))