Update dev-util/strace to v6.15. In this change dev-util/strace is updated to v6.15 as the older version failed to compile with th new glibc. Upstream gentoo renamed dev-util/strace to dev-debug/strace. This change also implements that rename. Change-Id: I8f9eeb8d3e8b819076fa722996f17982bc985082 Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/portage-stable/+/210368 Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com> Reviewed-by: Derek Taylor <ddtaylor@google.com>