llvm_tools: Fix cros workon invocation

At present, we invoke `cros workon` using the `cros-workon` style
syntax. This unfortunately:

1. Is going to be deprecated.
2. Doesn't work outside of the chroot.
3. Assumes you're working on the --host, when in fact you may
   not want to workon the host, you may want to workon a board.

This CL changes this behaviour, by not enabling cros workon by
default (warning the user it's not workon-ed), and using the
more modern cros workon syntax.

BUG=None
TEST=llvm_tools/setup_for_workon.py \
     --workon-board volteer-scudo \
     --package sys-libs/scudo
TEST=llvm_tools/setup_for_workon.py \
     --package sys-libs/scudo

Change-Id: I4f65c73ef12e64da973a14ec1ea9b9ea7b70b35f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/5321923
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Jordan Abrahams-Whitehead <ajordanr@google.com>
Tested-by: Jordan Abrahams-Whitehead <ajordanr@google.com>
1 file changed