[MacPorts] #69807: libjxl fails on 10.4: fatal error: spawn.h: No such file or directory

[MacPorts]

#69807: libjxl fails on 10.4: fatal error: spawn.h: No such file or directory
---------------------------+----------------------------
  Reporter:  barracuda156  |      Owner:  jmroot
      Type:  defect        |     Status:  assigned
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.9.3
Resolution:                |   Keywords:  tiger upstream
      Port:  libjxl        |
---------------------------+----------------------------

Comment (by barracuda156):

 By the way it also uses a wrong `environ` in the same file:
 {{{
 extern char** environ;  // NOLINT
 }}}

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Ticket URL: <https://trac.macports.org/ticket/69807#comment:3>
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