Make solns2out compile with older libstdc++
Make solns2out compile with older libstdc++

jjdekker/libminizinc,nathanielbaxter/libminizinc,tias/libminizinc,tias/libminizinc,jjdekker/libminizinc,nathanielbaxter/libminizinc,nathanielbaxter/libminizinc,jjdekker/libminizinc,jjdekker/libminizinc,nathanielbaxter/libminizinc