Hide test-only functions behind #[cfg(test)]

Author: kulp

src/features.rs

@@ -289,6 +289,7 @@ mod test {
         );
     }
 
+    #[cfg(test)]
     fn test_target(target_str: &str, target: RustTarget) {
         let target_string: String = target.into();
         assert_eq!(target_str, target_string);

src/ir/analysis/mod.rs

@@ -265,6 +265,7 @@ mod tests {
     struct Graph(HashMap<Node, Vec<Node>>);
 
     impl Graph {
+        #[cfg(test)]
         fn make_test_graph() -> Graph {
             let mut g = Graph::default();
             g.0.insert(Node(1), vec![Node(3)]);