Don't download cargo twice when download-rustc is set

Previously, this caused a bug on NixOS:

1. bootstrap.py would download and patch stage0/cargo
2. bootstrap.py would download nightly cargo, but extract it to
   stage0/cargo instead of ci-rustc/cargo.
3. bootstrap.py would fail to build rustbuild because stage0/cargo
   wasn't patched.

The "proper" fix is to extract nightly cargo to ci-rustc instead, but it
doesn't seem to be necessary at all, so this just skips downloading it
instead.

0 files changed, 0 insertions, 0 deletions