[MacPorts] #58930: gcc 8.3.0_4 with _XOPEN_SOURCE=500 breaks with #include <complex>

[MacPorts]

#58930: gcc 8.3.0_4 with _XOPEN_SOURCE=500 breaks with #include <complex>
-----------------------+--------------------
  Reporter:  bernstei  |      Owner:  (none)
      Type:  defect    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:  gcc8      |
-----------------------+--------------------

Comment (by kencu):

 My first thought was that this was an upstream issue, but it appears that
 at least some people feel that the way we build gcc on MacPorts is not
 fully correct in this area <https://github.com/arbor-
 sim/arbor/commit/3bafa1b3547d6102ca5376f6ce3bc00aab0280a2>, and it's a
 configuration bug (i.e. a MacPorts bug).

-- 
Ticket URL: <https://trac.macports.org/ticket/58930#comment:2>
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