Allow --source to be specified more than once

Author: theotherjimmy

tools/make.py

@@ -106,8 +106,8 @@
                       default=None, help="Required peripherals")
     parser.add_argument("--dep", dest="dependencies",
                       default=None, help="Dependencies")
-    group.add_argument("--source", dest="source_dir", type=argparse_filestring_type,
-                       default=None, help="The source (input) directory", nargs="*")
+    parser.add_argument("--source", dest="source_dir", type=argparse_filestring_type,
+                       default=None, help="The source (input) directory", action="append")
     parser.add_argument("--duration", type=int, dest="duration",
                       default=None, help="Duration of the test")
     parser.add_argument("--build", dest="build_dir",