Fix handling of GWT Incubator external package in build_externals

Signed-off-by: James Ren <jamesren@google.com>



git-svn-id: http://test.kernel.org/svn/autotest/trunk@4453 592f7852-d20e-0410-864c-8624ca9c26a4
diff --git a/utils/external_packages.py b/utils/external_packages.py
index 196964d..9f74655 100644
--- a/utils/external_packages.py
+++ b/utils/external_packages.py
@@ -740,7 +740,12 @@
     def _build_and_install(self, install_dir):
         dest = os.path.join(install_dir, GwtPackage.name, self.local_filename)
         shutil.copyfile(self.verified_package, dest)
-        os.symlink(dest, self.symlink_name)
+
+        symlink_path = os.path.join(
+                install_dir, GwtPackage.name, self.symlink_name)
+        if os.path.exists(symlink_path):
+            os.remove(symlink_path)
+        os.symlink(dest, symlink_path)
         return True