Fixed test_sqlpp_test_constraints to work with out of source build
Fixed test_sqlpp_test_constraints to work with out of source build

sergeken/sqlpp11,sergeken/sqlpp11,happybits/sqlpp11,rbock/sqlpp11,sergeken/sqlpp11,rbock/sqlpp11,happybits/sqlpp11,rettichschnidi/sqlpp11,happybits/sqlpp11,rbock/sqlpp11,volka/sqlpp11,rbock/sqlpp-concepts-experiments,rbock/sqlpp11,rbock/sqlpp-concepts-experiments,sergeken/sqlpp11,volka/sqlpp11,volka/sqlpp11,coldzhang/sqlpp11,volka/sqlpp11,happybits/sqlpp11,coldzhang/sqlpp11,rettichschnidi/sqlpp11,rettichschnidi/sqlpp11,rettichschnidi/sqlpp11,coldzhang/sqlpp11,rbock/sqlpp-concepts-experiments