iOS: Ensure that the rename-main logic works for multi-arch builds

We need to tell Xcode which architectures it should set up pre-link
dependencies for, as well as run the rename script in the root object
file directory. We pass it the current architectures so that we only
rename main() for simulator or device, not both.

Change-Id: I095d7c8a22ff0cb2ce872c9a86c93a070c1fcc65
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>