[MacPorts] #64620: gcc 10 fails to build on 10.13

[MacPorts]

#64620: gcc 10 fails to build on 10.13
-----------------------+----------------------
 Reporter:  JohnFHall  |      Owner:  (none)
     Type:  defect     |     Status:  assigned
 Priority:  Normal     |  Milestone:
Component:  ports      |    Version:  2.7.1
 Keywords:             |       Port:
-----------------------+----------------------
 :info:build /opt/local/var/macports/build

 /_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc10/gcc10/work/build/x86_64
 -apple-darwin17/libstdc++-v3/include/bits/basic_string.h:48:11: fatal
 error: string_view: No such file or directory

 :info:build    48 | # include <string_view>

 :info:build       |           ^~~~~~~~~~~~~

 :info:build compilation terminated.

-- 
Ticket URL: <https://trac.macports.org/ticket/64620>
MacPorts <https://www.macports.org/>
Ports system for macOS