[MacPorts] #43939: libpng: pngconf.h:366:52: error: token is not a valid binary operator in a preprocessor subexpression

[MacPorts]

#43939: libpng: pngconf.h:366:52: error: token is not a valid binary operator in a
preprocessor subexpression
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  Reporter:  macports@…  |      Owner:  ryandesign@…
      Type:  defect      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.3.0
Resolution:              |   Keywords:
      Port:  libpng      |
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Comment (by ryandesign@…):

 He said "MacPro", all of which are 64-bit. I'm guessing he has an older
 version of Xcode, with an older version of clang, before they added
 support for `__has_attribute`. I can try installing an older Xcode on my
 Snow Leopard machine.

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Ticket URL: <https://trac.macports.org/ticket/43939#comment:11>
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