[tor-bugs] #25719 [Applications/rbm]: Add option to store last time a file was used in a build

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#25719: Add option to store last time a file was used in a build
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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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 In `tor-browser-build`, we can clean old build files by running `make
 clean`, which will keep only the files used in the current build.

 There are however some problems with that:
 - running `make clean` is slow as it needs to compute all the file names
 used in a build, for all the branches/series we are using.
 - when working on different bugs at the same time, running `make clean`
 will clean build files created by branches that have not been merged yet.

 Instead, it would be nice to be able to clean files that have not been
 used in the last X days. To allow that, rbm should have an option to store
 somewhere a timestamp of when each input files have been used in a build
 for the last time.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25719>
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