scripts: package rustc and cargo

These were probably dropped last year, when we split `rust` and
`rust-host` into separate packages. It seems this broke a user of them.

We don't officially support the functionality of these, but we have
promised to ship them as a part of this tarball; this CL helps us make
good on that promise.

BUG=b:269306499
TEST=cros_setup_toolchains produces tarballs with these. Running
     `./rustc --help` and `./cargo --help` works.

Change-Id: I0b3c160dd1388bf16dcf459ca1d85c7a7bf91311
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4249801
Tested-by: George Burgess <gbiv@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index 38cff61..b69ba81 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -129,11 +129,16 @@
     # Packages that needs separate handling, in addition to what we have from
     # crossdev.
     MANUAL_PKGS = {
-        "rust": "dev-lang",
         "llvm": "sys-devel",
         "llvm-libunwind": "sys-libs",
         "libcxx": "sys-libs",
         "elfutils": "dev-libs",
+        # b/269306499: note that rust and rust-host are shipped as a part of
+        # this tarball on a best-effort basis. If you would like them to be
+        # fully supported (with an SLA), please reach out to
+        # chromeos-toolchain@google.com and chat with us.
+        "rust": "dev-lang",
+        "rust-host": "dev-lang",
     }
 
     @classmethod