This allows greater granular control over the release
build, and avoids WITH_FOO=1 and WITHOUT_FOO=1 collision.
This change was verified to produce correct results
compared to an earlier build by diffing find(1) output
of the resulting bootonly/, dvd/, and release/ directories.
Tested on: head@r267449
MFC after: 1 month
X-MFC-Note: Requires commits not yet MFC'd, so likely
longer than 1 month.
Sponsored by: The FreeBSD Foundation
9b3c9d611e