auto merge of #5332 : jdm/rust/transitivelink, r=graydon

The original change bit Servo because rust-harfbuzz includes libharfbuzz.a in its link_args. This works fine in the rust-harfbuzz subdirectory where the static library resides, but when this is propagated to servo_gfx, the lirbrary can no longer be found since it's a relative path.

src/librustc/back/link.rs

@@ -818,7 +818,11 @@ fn unlib(config: @session::config, +stem: ~str) -> ~str {
     do cstore::iter_crate_data(cstore) |crate_num, _| {
         let link_args = csearch::get_link_args_for_crate(cstore, crate_num);
         do vec::consume(link_args) |_, link_arg| {
-            cc_args.push(link_arg);
+            // Linker arguments that don't begin with - are likely file names,
+            // so they should not be necessary.
+            if link_arg.starts_with("-") {
+              cc_args.push(link_arg);
+            }
         }
     }