llvm_tools: Add default value for dependent CLs

Use [] as a default value to avoid non-iterable type
errors.

BUG=chromium:1067029
TEST=unit tests

Change-Id: Ibc4c76c2dcda8e3846d323345aeea49ac2e9acaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2148005
Reviewed-by: George Burgess <gbiv@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
1 file changed