Add new test to highlight namespace for self import

gcc/testsuite/ChangeLog:

	* rust/compile/self_import_namespace.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Author: P-E-P

gcc/testsuite/rust/compile/self_import_namespace.rs

@@ -0,0 +1,14 @@
+// { dg-additional-options "-frust-name-resolution-2.0" }
+
+mod bar {
+    pub mod foo {}
+    pub fn foo() {}
+}
+
+// This only imports the module `foo`. The function `foo` lives in
+// the value namespace and is not imported.
+use bar::foo::{self};
+
+fn main() {
+    foo(); // { dg-error "expected value" }
+}