Is there some special reason to use cppoptlib from 2018 instead of the current one?

[barracuda156]

polysolve does not build with the current version of cppoptlib, since its headers structure was changed since 2018, and this one does not exist:

In file included from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Problem.cpp:1:
/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Problem.hpp:7:10: fatal error: cppoptlib/problem.h: No such file or directory
    7 | #include <cppoptlib/problem.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/polysolve.dir/src/polysolve/nonlinear/Problem.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
In file included from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/DescentStrategy.hpp:5,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Solver.hpp:3,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Solver.cpp:2:
/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Problem.hpp:7:10: fatal error: cppoptlib/problem.h: No such file or directory
    7 | #include <cppoptlib/problem.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
In file included from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/DescentStrategy.hpp:5,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/BFGS.hpp:5,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/BFGS.cpp:3:
/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Problem.hpp:7:10: fatal error: cppoptlib/problem.h: No such file or directory
    7 | #include <cppoptlib/problem.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
In file included from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/DescentStrategy.hpp:5,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/LBFGS.hpp:5,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/LBFGS.cpp:3:
/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Problem.hpp:7:10: fatal error: cppoptlib/problem.h: No such file or directory
    7 | #include <cppoptlib/problem.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/polysolve.dir/src/polysolve/nonlinear/Solver.cpp.o] Error 1
make[2]: *** [CMakeFiles/polysolve.dir/src/polysolve/nonlinear/descent_strategies/BFGS.cpp.o] Error 1
In file included from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/descent_strategies/DescentStrategy.hpp:5,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Solver.hpp:3,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/BoxConstraintSolver.hpp:3,
                 from /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/BoxConstraintSolver.cpp:1:
/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_math_polysolve/polysolve/work/polysolve-73d98008631b8ae1617131cb4896f784ae2ec5fe/src/polysolve/nonlinear/Problem.hpp:7:10: fatal error: cppoptlib/problem.h: No such file or directory
    7 | #include <cppoptlib/problem.h>
      |          ^~~~~~~~~~~~~~~~~~~~~

Is there some special reason to stay with the legacy version of this library or is it possible to amend the sources to use the current one?

(Or if the license allows, just bundle whatever headers are needed and drop an external dependency on it.)