[tor-bugs] #21931 [Applications/Tor Browser]: backport OSX SetupMacCommandLine updater fixes

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#21931: backport OSX SetupMacCommandLine updater fixes
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     Reporter:  mcs                       |      Owner:  tbb-team
         Type:  defect                    |     Status:  new
     Priority:  Medium                    |  Milestone:
    Component:  Applications/Tor Browser  |    Version:
     Severity:  Normal                    |   Keywords:
Actual Points:                            |  Parent ID:
       Points:                            |   Reviewer:
      Sponsor:                            |
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 While testing the updater with an ad hoc (non-gitian) build, Kathy and I
 ran into https://bugzilla.mozilla.org/show_bug.cgi?id=1335916. With
 gitian-based builds (which are compiled and linked with an older OSX SDK
 than our ad hoc ones are), the code does not crash but it does emit a
 warning:
  WARNING: nextEventMatchingMask should only be called from the Main
 Thread! This will throw an exception in the future.

 We should backport the Mozilla fix for 1335916, as well as a follow up fix
 from https://bugzilla.mozilla.org/show_bug.cgi?id=1342887.

 I will create a branch that contains the cherry picked patches.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21931>
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