Add ro.build.system_root_image

ro.build.system_root_image is true if the root directory is built
into the system image.

Change-Id: I17208ebd004c63aebb09db6c3e5f795619e73bd2
diff --git a/tools/buildinfo.sh b/tools/buildinfo.sh
index 5c199b8..1329be7 100755
--- a/tools/buildinfo.sh
+++ b/tools/buildinfo.sh
@@ -20,6 +20,9 @@
 echo "ro.build.host=`hostname`"
 echo "ro.build.tags=$BUILD_VERSION_TAGS"
 echo "ro.build.flavor=$TARGET_BUILD_FLAVOR"
+if [ -n "$BOARD_BUILD_SYSTEM_ROOT_IMAGE" ] ; then
+  echo "ro.build.system_root_image=$BOARD_BUILD_SYSTEM_ROOT_IMAGE"
+fi
 echo "ro.product.model=$PRODUCT_MODEL"
 echo "ro.product.brand=$PRODUCT_BRAND"
 echo "ro.product.name=$PRODUCT_NAME"