auto merge of #12688 : alexcrichton/rust/fix-some-link-args, r=brson

Linker argument order with respect to libraries is important enough that we
shouldn't be attempting to filter out libraries getting passed through to the
linker. When linking with a native library that has multiple dependant native
libraries, it's useful to have control over the link argument order.

src/test/run-make/no-duplicate-libs/Makefile

@@ -0,0 +1,6 @@
+-include ../tools.mk
+
+all: $(call STATICLIB,foo) $(call STATICLIB,bar)
+	$(RUSTC) main.rs
+	$(call RUN,main)
+

src/test/run-make/no-duplicate-libs/bar.c

@@ -0,0 +1,3 @@
+extern void foo();
+
+void bar() { foo(); }

src/test/run-make/no-duplicate-libs/foo.c

@@ -0,0 +1 @@
+void foo() {}

src/test/run-make/no-duplicate-libs/main.rs

@@ -0,0 +1,20 @@
+// 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.
+
+#[link(name = "foo")]
+#[link(name = "bar")]
+#[link(name = "foo")]
+extern {
+    fn bar();
+}
+
+fn main() {
+    unsafe { bar() }
+}