rustc_back: Don't pass 'u' to ar invocations

This flag indicates that when files are being replaced or added to archives (the
`r` flag) that the new file should not be inserted if it is not newer than the
file that already exists in the archive. The compiler never actually has a use
case of *not* wanting to insert a file because it already exists, and this
causes rlibs to not be updated in some cases when the compiler was re-run too
quickly.

Closes #18913

Author: alexcrichton

Diff for: src/librustc_back/archive.rs

@@ -259,7 +259,7 @@ impl<'a> ArchiveBuilder<'a> {
                 // Add the archive members seen so far, without updating the
                 // symbol table (`S`).
                 run_ar(self.archive.handler, &self.archive.maybe_ar_prog,
-                       "cruS", Some(self.work_dir.path()), &args[..]);
+                       "crS", Some(self.work_dir.path()), &args[..]);
 
                 args.clear();
                 args.push(&abs_dst);
@@ -272,7 +272,7 @@ impl<'a> ArchiveBuilder<'a> {
 
         // Add the remaining archive members, and update the symbol table if
         // necessary.
-        let flags = if self.should_update_symbols { "crus" } else { "cruS" };
+        let flags = if self.should_update_symbols { "crs" } else { "crS" };
         run_ar(self.archive.handler, &self.archive.maybe_ar_prog,
                flags, Some(self.work_dir.path()), &args[..]);
 

Diff for: src/test/auxiliary/issue-18913-1.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 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.
+
+// no-prefer-dynamic
+
+#![crate_type = "rlib"]
+#![crate_name = "foo"]
+
+pub fn foo() -> i32 { 0 }

Diff for: src/test/auxiliary/issue-18913-2.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 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.
+
+// no-prefer-dynamic
+
+#![crate_type = "rlib"]
+#![crate_name = "foo"]
+
+pub fn foo() -> i32 { 1 }

Diff for: src/test/run-pass/issue-18913.rs

@@ -0,0 +1,18 @@
+// Copyright 2015 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.
+
+// aux-build:issue-18913-1.rs
+// aux-build:issue-18913-2.rs
+
+extern crate foo;
+
+fn main() {
+    assert_eq!(foo::foo(), 1);
+}