cmake: add transitive dependency on legacy-option-headers

cmake: add transitive dependency on legacy-option-headers

the legacy-option-headers target is only marked as a dependency of the
common-objs and common-common-objs. because those targets are OBJECT
libraries, their dependencies aren't inherited by the targets that link
common-objs or common-common-objs

this adds the dependencies manually, so that changes to the config
yaml files will cause legacy-option-headers to regenerate the headers

Signed-off-by: Casey Bodley <cbodley@redhat.com>