[MacPorts] #53097: kchmviewer: upgrade to v7.7 and Qt 5.6

[MacPorts]

#53097: kchmviewer: upgrade to v7.7 and Qt 5.6
----------------------+------------------------
 Reporter:  RJVB      |      Owner:
     Type:  update    |     Status:  new
 Priority:  Normal    |  Milestone:
Component:  ports     |    Version:
 Keywords:  haspatch  |       Port:  kchmviewer
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 port:kchmviewer has been long obsolete and might not even build anymore on
 recent OS X versions.

 The attached patch updates the port to the current 7.7 version and builds
 it against Qt5. It works quite nicely, both with "real Win32" .chm files
 and with Doxygen documents converted to .chm with `chmcmd`.

 A number of the patches required to get this to build and function as
 intended have already been submitted upstream. They can be found here:
 https://github.com/RJVB/macstrop/tree/master/devel/kchmviewer/files

 See also #53077.

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Ticket URL: <https://trac.macports.org/ticket/53097>
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