[MacPorts] #55469: snowleopard_fixes portgroup behavior changed, causing some ports to fail to build

[MacPorts]

#55469: snowleopard_fixes portgroup behavior changed, causing some ports to fail to
build
-------------------------+-------------------
  Reporter:  ryandesign  |      Owner:  kencu
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:              |
-------------------------+-------------------

Comment (by ryandesign):

 Ok yes, I was just thinking that it would probably be ok if the procedure
 that's called later ''only'' adds the dependencies, and it looks like
 that's what Marcus did in cxx11 1.1. The flags are modified immediately
 (when the portgroup is included). If snowleopard_fixes did the same that
 should work.

 Up to now, we've told portfile authors to append to dependencies if they
 include a portgroup, but time and again we find portfile authors who don't
 do that. If we can find a way to make it so that portfile authors don't
 need to do that, as I think this fix is trying to do, that's great. And we
 should do it in all the portgroups. But first maybe we should make
 `port::register_callback` available in the portfile's namespace so that we
 don't need to use a proc name with `:`s.

--
Ticket URL: <https://trac.macports.org/ticket/55469#comment:3>
MacPorts <https://www.macports.org/>
Ports system for macOS