The provisions of this article shall not apply to the construction of any public building used for facilities of juvenile forestry camps or juvenile homes, ranches, or camps established under Article 15 (commencing with Section 880) of Chapter 2, Part 1, Division 2 of the Welfare and Institutions Code, if a major portion of the construction work is to be performed by wards of the juvenile court assigned to such camps, ranches, or homes; or to public projects employing prisoners pursuant to Section 25359 of the Government Code and public projects involving persons engaged in federal, state, or county job or work training programs.