[tor-bugs] #30039 [Applications/rbm]: Add options to be able to prepend or append targets

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#30039: Add options to be able to prepend or append targets
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     Reporter:  boklm             |      Owner:  boklm
         Type:  task              |     Status:  new
     Priority:  Medium            |  Milestone:
    Component:  Applications/rbm  |    Version:
     Severity:  Normal            |   Keywords:  tbb-rbm
Actual Points:                    |  Parent ID:
       Points:                    |   Reviewer:
      Sponsor:                    |
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 When listing an other project in `input_files`, it is possible to specify
 other targets which will be used to build this project.

 In `tor-browser-build` we do this for example in `projects/https-
 everywhere/config` to use the `common-stretch` target and avoid building a
 different python for each platform.

 The issue however with setting `target` is that it is replacing any
 previous target. In many cases however it would be useful to keep the
 previous targets and only append or prepend some other targets.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30039>
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