Require that TOOLKIT_VERSION be set externally

This change removes the default value for TOOLKIT_VERSION and checks that this
is set. A warning is also issued if the package TAGS do not match.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

Makefile

@@ -16,8 +16,18 @@ LIB_NAME := nvidia-docker2
 LIB_VERSION := 2.8.0
 LIB_TAG ?= rc.1
 
-TOOLKIT_VERSION ?= 1.7.0
-TOOLKIT_TAG ?= $(LIB_TAG)
+# Define the nvidia-container-toolkit version on which the nvidia-docker2
+# package depends. It is recommended that the TOOLKIT_TAG and the LIB_TAG match.
+TOOLKIT_VERSION ?= # Set by CI
+TOOLKIT_TAG ?= # Set by CI
+
+ifeq ($(strip $(TOOLKIT_VERSION)),)
+$(error TOOLKIT_VERSION must be specified)
+endif
+
+ifneq ($(TOOLKIT_TAG),$(LIB_TAG))
+$(warning TOOLKIT_TAG=$(TOOLKIT_TAG) and LIB_TAG=$(LIB_TAG) do not match)
+endif
 
 # By default run all native docker-based targets
 docker-native: