build: Make 'clean' idempotent
build: Make 'clean' idempotent

Running make clean twice in a row is an error as rm hack/virtc/virc
will fail trying to remove an nonexistent binary.

Signed-off-by: Damien Lespiau <64bd3cb94f359c1a3ce68dae5e26b40578526277@intel.com>

containers/virtcontainers,wcwxyz/virtcontainers,containers/virtcontainers,wcwxyz/virtcontainers,wcwxyz/virtcontainers