taking reasonable cost savings measures, as determined by the Secretary, would otherwise be required to terminate rental assistance for families as a result of insufficient funding: Provided further , That of the amounts made available under this heading in this Act, $1,000,000,000 shall be used for incremental rental voucher assistance under section 8(o) of the United States Housing Act of 1937 for use by individuals and families who are—homeless, as defined under section 103(a) of the McKinney-Vento Homeless Assistance Act ( 42 U.S.C. 11302(a) )