tools/hardlink_packages: Check that the package_repo command exists.

src/tools/hardlink_packages.py

@@ -4,7 +4,7 @@
 # Hardlink only packages used in the build from one directory to another,
 # and updates the RemotePackageRepository file at the same time.
 #
-# Copyright 2017 Augustin Cavalier <waddlesplash>
+# Copyright 2017-2019 Augustin Cavalier <waddlesplash>
 # Distributed under the terms of the MIT License.
 
 import sys, os, re, hashlib
@@ -17,6 +17,10 @@ if len(sys.argv) < 5:
 		+ " and a repo.info.template file (using $ARCH$)")
 	sys.exit(1)
 
+if os.system('package_repo') != 1:
+	print("package_repo command does not seem to exist.")
+	sys.exit(1)
+
 args_arch = sys.argv[1]
 args_jamf = sys.argv[2]
 args_src = sys.argv[3]