[MacPorts] #70650: mdtree-cpp needs filesystem support in compiler

[MacPorts]

#70650: mdtree-cpp needs filesystem support in compiler
--------------------------+-------------------------
 Reporter:  barracuda156  |      Owner:  herbygillot
     Type:  defect        |     Status:  assigned
 Priority:  Normal        |  Milestone:
Component:  ports         |    Version:  2.10.1
 Keywords:                |       Port:  mdtree-cpp
--------------------------+-------------------------
 {{{
 [ 50%] Building CXX object CMakeFiles/mdtree.dir/mdtree.cpp.o
 /usr/bin/clang++   -pipe -Os -DNDEBUG -I/opt/local/include -stdlib=libc++
 -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk
 -std=gnu++2a -arch x86_64 -isysroot
 /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk -mmacosx-version-
 min=10.14 -MD -MT CMakeFiles/mdtree.dir/mdtree.cpp.o -MF
 CMakeFiles/mdtree.dir/mdtree.cpp.o.d -o CMakeFiles/mdtree.dir/mdtree.cpp.o
 -c /opt/local/var/macports/build
 /_opt_bblocal_var_buildworker_ports_build_ports_textproc_mdtree-cpp
 /mdtree-cpp/work/1.0.0/mdtree.cpp
 In file included from /opt/local/var/macports/build
 /_opt_bblocal_var_buildworker_ports_build_ports_textproc_mdtree-cpp
 /mdtree-cpp/work/1.0.0/mdtree.cpp:1:
 /opt/local/var/macports/build
 /_opt_bblocal_var_buildworker_ports_build_ports_textproc_mdtree-cpp
 /mdtree-cpp/work/1.0.0/mdtree.h:11:10: fatal error: 'filesystem' file not
 found
 #include <filesystem>
          ^~~~~~~~~~~~
 1 error generated.
 }}}

 I have nothing to test this locally on (modern gcc supports `filesystem`
 out of the box), but looks like it needs `legacysupport` help here :)

-- 
Ticket URL: <https://trac.macports.org/ticket/70650>
MacPorts <https://www.macports.org/>
Ports system for macOS