[MacPorts] #64745: Update compiler selection for newer standards

[MacPorts]

#64745: Update compiler selection for newer standards
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 Reporter:  ctreleaven   |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:
 Keywords:               |       Port:
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 Upstream projects are now starting to require C++20 which is not currently
 supported in base.  For example, the vte project switched to GNU++20
 around Feb 2021:

 https://gitlab.gnome.org/GNOME/vte/-/blob/master/meson.build

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Ticket URL: <https://trac.macports.org/ticket/64745>
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