Fix staticlib outputs linking to blank archives

src/librustc/back/archive.rs

@@ -173,6 +173,7 @@ impl Archive {
             if_ok!(fs::rename(file, &new_filename));
             inputs.push(new_filename);
         }
+        if inputs.len() == 0 { return Ok(()) }
 
         // Finally, add all the renamed files to this archive
         let mut args = ~[&self.dst];

src/test/run-make/staticlib-blank-lib/Makefile

@@ -0,0 +1,6 @@
+-include ../tools.mk
+
+all:
+	ar crus libfoo.a foo.rs
+	ar d libfoo.a foo.rs
+	$(RUSTC) foo.rs

src/test/run-make/staticlib-blank-lib/foo.rs

@@ -0,0 +1,16 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[crate_type = "staticlib"];
+
+#[link(name = "foo", kind = "static")]
+extern {}
+
+fn main() {}