[MacPorts] #61488: multiple ports: review macOS version checking

[MacPorts]

#61488: multiple ports: review macOS version checking
-------------------------+-------------------------------------------------
 Reporter:  jmroot       |      Owner:  (none)
     Type:  defect       |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:               |       Port:  icu-le-hb libassuan libgcrypt isl
                         |  libdaemon cloog gdbm db60 db48 net-snmp hdf4
                         |  gsl gcc46 gcc48 gcc49 gcc47 gcc45 gcc44
                         |  libcanberra sox xorg-libXxf86vm libart_lgpl
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 All these ports have a patch called `yosemite-libtool.patch` which adjusts
 the macOS version checking so it correctly recognises 10.x versions above
 10.9. They should be reviewed for macOS 11.0 compatibility. If there is a
 problem, they will fail to build on Big Sur due to undefined symbols. If
 they don't fail to build, they must not actually need to allow undefined
 symbols and no action is needed AFAICT, as the existing code won't use
 -flat_namespace on unrecognised versions.

 Failing ports should be patched the same way that libtool has been:
 https://github.com/macports/macports-
 ports/blob/master/devel/libtool/files/dynamic_lookup-11.patch

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Ticket URL: <https://trac.macports.org/ticket/61488>
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