Add test for constructing in a Texp_hole

Author: liam923

tests/test-dirs/construct/c-simple.t

@@ -586,3 +586,14 @@ Test M.3 : Predef types
   [
     "(lazy _)"
   ]
+
+Test M.4 : that construct will work on holes in an overwrite expression
+
+  $ cat > M4.ml <<EOF
+  > let _ = overwrite_ (1, 2) with (_, 3)
+  > EOF
+
+TODO: fix this
+  $ $MERLIN single construct -position 1:32 \
+  > -filename M4.ml < M4.ml | jq .value
+  "Construct only works on holes."