Notice non-toplevel dll dependencies in rustbuild

Previously Cargo would hardlink all the dependencies into the "root" as
foo.dll and the `toplevel` array would get populated with these, but
that's no longer the case. Instead, cargo will only do this for the
final artifacts/final libraries.

Rustbuild is updated to continue looping through the artifacts mentioned
instead of early-returning. This should fix the bug.

@alexcrichton found the cause of this and suggested this fix.

src/bootstrap/compile.rs

@@ -1049,22 +1049,22 @@ pub fn run_cargo(builder: &Builder, cargo: &mut Command, stamp: &Path, is_check:
                !filename.ends_with(".lib") &&
                !is_dylib(&filename) &&
                !(is_check && filename.ends_with(".rmeta")) {
-                return;
+                continue;
             }
 
             let filename = Path::new(&*filename);
 
             // If this was an output file in the "host dir" we don't actually
             // worry about it, it's not relevant for us.
             if filename.starts_with(&host_root_dir) {
-                return;
+                continue;
             }
 
             // If this was output in the `deps` dir then this is a precise file
             // name (hash included) so we start tracking it.
             if filename.starts_with(&target_deps_dir) {
                 deps.push(filename.to_path_buf());
-                return;
+                continue;
             }
 
             // Otherwise this was a "top level artifact" which right now doesn't