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:

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gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
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Copyright (C) 2021 Free Software Foundation, Inc.
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This is free software; see the source for copying conditions.  There is NO
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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.