Add a regression test for channels of nil, which happens to work in rustc, but not in rustboot

Makefile.in

@@ -501,6 +501,7 @@ TASK_XFAILS := $(addprefix $(S)src/test/run-pass/, \
                  task-comm-12.rs \
                  task-comm-2.rs \
                  task-comm-9.rs \
+                 task-comm-chan-nil.rs \
                  task-life-0.rs \
                  alt-type-simple.rs \
                  many.rs)

src/Makefile

@@ -434,6 +434,7 @@ TASK_XFAILS := test/run-pass/task-comm-8.rs \
                test/run-pass/task-comm-12.rs \
                test/run-pass/task-comm-2.rs \
                test/run-pass/task-comm-9.rs \
+               test/run-pass/task-comm-chan-nil.rs \
                test/run-pass/task-life-0.rs \
                test/run-pass/alt-type-simple.rs \
                test/run-pass/many.rs

src/test/run-pass/task-comm-chan-nil.rs

@@ -0,0 +1,17 @@
+// -*- rust -*-
+
+// rustboot can't transmit nils across channels because they don't have
+// any size, but rustc currently can because they do have size. Whether
+// or not this is desirable I don't know, but here's a regression test.
+
+impure fn main() {
+  let port[()] po = port();
+  let chan[()] ch = chan(po);
+
+  ch <| ();
+
+  let () n;
+  n <- po;
+
+  check (n == ());
+}