[MacPorts] #59224: gcc8 @8.3.0_4: build broken on Catalina or Mojave against 10.15 SDK due to unrecognized header macro __OSX_AVAILABLE_STARTING

[MacPorts]

#59224: gcc8 @8.3.0_4: build broken on Catalina or Mojave against 10.15 SDK due to
unrecognized header macro __OSX_AVAILABLE_STARTING
--------------------------+----------------------
  Reporter:  MaddTheSane  |      Owner:  (none)
      Type:  defect       |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:  2.6.1
Resolution:               |   Keywords:  catalina
      Port:  gcc8         |
--------------------------+----------------------

Comment (by cjones051073):

 Note the latest comments fro Jeremy in

 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90835

 Reads to me that this bug fell between the cracks somehow, but is being
 looked into now. So I would hope an Xcode update at some point might
 address it.

 Until then, yes, it might be worth adding a pre fetch check and a useful
 message, if only to prevent more tickets in the meantime...

-- 
Ticket URL: <https://trac.macports.org/ticket/59224#comment:7>
MacPorts <https://www.macports.org/>
Ports system for macOS