Add tests.

src/test/compile-fail/linkage4.rs

@@ -0,0 +1,15 @@
+// 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.
+
+#[linkage = "external"]
+static foo: int = 0;
+//~^ ERROR: the `linkage` attribute is experimental and not portable
+
+fn main() {}

src/test/run-make/linkage-attr-on-static/Makefile

@@ -0,0 +1,8 @@
+-include ../tools.mk
+
+all:
+	$(CC) foo.c -c -o $(TMPDIR)/foo.o
+	$(AR) rcs $(TMPDIR)/libfoo.a $(TMPDIR)/foo.o
+	$(RUSTC) bar.rs -lfoo -L $(TMPDIR)
+	$(call RUN,bar) || exit 1
+

src/test/run-make/linkage-attr-on-static/bar.rs

@@ -0,0 +1,25 @@
+// 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.
+
+#![feature(linkage)]
+
+#[no_mangle]
+#[linkage = "external"]
+static BAZ: i32 = 21;
+
+extern {
+    fn what() -> i32;
+}
+
+fn main() {
+    unsafe {
+        assert_eq!(what(), BAZ);
+    }
+}

src/test/run-make/linkage-attr-on-static/foo.c

@@ -0,0 +1,7 @@
+#include <stdint.h>
+
+extern int32_t BAZ;
+
+int32_t what() {
+    return BAZ;
+}