[MacPorts] #70367: dia fails to link: Undefined symbols: "_png_get_header_ver"

[MacPorts]

#70367: dia fails to link: Undefined symbols: "_png_get_header_ver"
---------------------------+--------------------
  Reporter:  barracuda156  |      Owner:  (none)
      Type:  defect        |     Status:  new
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.9.3
Resolution:                |   Keywords:
      Port:  dia           |
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Comment (by ryandesign):

 That symbol is probably from libpng and the error is probably occurring
 because `-lpng` is not in the link line.

 We had successful builds of this port on all buildbot systems so we'll
 need to see your main.log file to try to figure out what's different on
 your system.

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Ticket URL: <https://trac.macports.org/ticket/70367#comment:1>
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