Migrate hermetic C++ toolchain to use self-extracting binary.

BUG=b:291840720
TEST=portage/tools/run_tests.sh

Change-Id: Id13437c3efad6c57abc48c0b620c54937d15ec9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/bazel/+/5581477
Auto-Submit: Matt Stark <msta@google.com>
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
2 files changed