Use "" in the native_name as an indication that no extra options have to

be passed to the "linker". Use that for libc.

src/comp/driver/session.rs

@@ -125,6 +125,9 @@ obj session(ast::crate_num cnum,
     }
     fn has_external_crate(int num) -> bool { ret crates.contains_key(num); }
     fn add_used_library(&str lib) {
+        if (lib == "") {
+            ret;
+        }
         // A program has a small number of libraries, so a vector is probably
         // a good data structure in here.
         for (str l in used_libraries) {