Preserve symlinks when installing
Preserve symlinks when installing

The lldb-preview component includes symlinks.  Currently, rustup
changes these to be regular files while installing.  This then causes
the resulting lldb to load liblldb twice, which causes a crash at
startup, because command line options are registered twice.  This
changes rustup to preserve symlinks when installing.

inejge/rustup.rs,nodakai/rustup.rs,rust-lang/rustup,inejge/rustup.rs,inejge/rustup.rs,rust-lang/rustup,rust-lang/rustup,inejge/rustup.rs,nodakai/rustup.rs,inejge/rustup.rs,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,nodakai/rustup.rs,rust-lang/rustup