Allow /usr/crosstool to exist in EdgeOS builds

BUG=b/290986313
TEST=Built a VM image with this and didn't get shot down by hook script
RELEASE_NOTE=None

Change-Id: I3b3256668dc5a600adadacc89ac6bbe5e066b194
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/62574
Reviewed-by: Alan Berryhill <berryhill@google.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>