shapelib @1.6.1 -- Unable to build -- fatal error: 'filesystem' file not found

[RobK88]

I am unable to upgrade / build shapelib in High Sierra -- fatal error: 'filesystem' file not found

...

Building CXX object tests/CMakeFiles/dbf_test.dir/dbf_test.cc.o
cd /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build/tests && /usr/bin/clang++  -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/shapelib-1.6.1 -isystem /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build/_deps/googletest-src/googletest/include -isystem /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build/_deps/googletest-src/googletest -pipe -Os -DNDEBUG -I/opt/local/include -stdlib=libc++ -std=c++17 -arch x86_64 -mmacosx-version-min=10.13 -MD -MT tests/CMakeFiles/dbf_test.dir/dbf_test.cc.o -MF CMakeFiles/dbf_test.dir/dbf_test.cc.o.d -o CMakeFiles/dbf_test.dir/dbf_test.cc.o -c /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/shapelib-1.6.1/tests/dbf_test.cc
/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/shapelib-1.6.1/tests/sbn_test.cc:3:10: fatal error: 'filesystem' file not found
#include <filesystem>
         ^~~~~~~~~~~~
/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/shapelib-1.6.1/tests/dbf_test.cc:4:10: fatal error: 'filesystem' file not found
#include <filesystem>
         ^~~~~~~~~~~~
1 error generated.
make[2]: *** [tests/CMakeFiles/sbn_test.dir/sbn_test.cc.o] Error 1
make[2]: Leaving directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build'
make[1]: *** [tests/CMakeFiles/sbn_test.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
1 error generated.
make[2]: *** [tests/CMakeFiles/dbf_test.dir/dbf_test.cc.o] Error 1
make[2]: Leaving directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build'
make[1]: *** [tests/CMakeFiles/dbf_test.dir/all] Error 2
make[1]: Leaving directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build'
make: *** [all] Error 2
make: Leaving directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build'
Command failed:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/work/build" && /usr/bin/make -j2 -w all VERBOSE=ON 
Exit code: 2
Error: Failed to build shapelib: command execution failed
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_shapelib/shapelib/main.log for details.
Error: Follow https://guide.macports.org/#project.tickets if you believe there is a bug.

[RobK88]

main.log