mk: Parameterize tests.mk to the max

Author: brson

configure

@@ -624,7 +624,7 @@ do
     make_dir $h/test/doc-tutorial-macros
     make_dir $h/test/doc-tutorial-borrowed-ptr
     make_dir $h/test/doc-tutorial-tasks
-    make_dir $h/test/doc-ref
+    make_dir $h/test/doc-rust
 done
 
 # Configure submodules