Revert "Move to c++17 for pqxx"

irdb-libs/dump_insns/SConscript

irdb-libs/dump_map/SConscript

irdb-libs/ir_builders/SConscript

irdb-libs/libEXEIO/src/SConscript

irdb-libs/libEXEIO/test/SConscript

irdb-libs/libIRDB-cfg/src/SConscript

irdb-libs/libIRDB-core/src/SConscript

irdb-libs/libIRDB-deep/src/SConscript

irdb-libs/libIRDB-elfdep/src/SConscript

irdb-libs/libIRDB-elfdep/test/SConscript

irdb-libs/libIRDB-syscall/src/SConscript

irdb-libs/libIRDB-transform/src/SConscript

irdb-libs/libIRDB-util/src/SConscript

irdb-libs/libMEDSannotation/SConscript

irdb-libs/meds2pdb/SConscript

irdb-libs/thanos/SConscript

zipr_push64_reloc_plugin/SConscript

zipr_unpin_plugin/SConscript