Build legacy branch

On Linux julyfun-Lenovo-XiaoXinAir-14IIL-2020 5.19.0-46-generic #47~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Jun 21 15:35:31 UTC 2 x86_64 x86_64 x86_64 GNU/Linux, 2024-1-25, and gcc:

gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Building legacy branch under CXX 14 17 & 20 can meet syntax errors which seem like cpp standard errors.

Unsolved.