[lld] Prefer printf over echo -e
Otherwise we break some MacOS bots when using the lit internal shell
because /bin/echo on MacOS does not support -e. Using the external shell
we end up using the echo builtin to /bin/bash, which does support this.
The echo builtin implementation in lit does support this, but that is
currently not enabled in pipelines. Might be worth looking into fixing
at some point.
