[tor-bugs] #23689 [- Select a component]: Add GitLab CI script

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#23689: Add GitLab CI script
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     Reporter:  krichter              |      Owner:  (none)
         Type:  enhancement           |     Status:  new
     Priority:  Medium                |  Milestone:
    Component:  - Select a component  |    Version:
     Severity:  Normal                |   Keywords:
Actual Points:                        |  Parent ID:
       Points:                        |   Reviewer:
      Sponsor:                        |
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 As [suggested and merged for
 tor](https://trac.torproject.org/projects/tor/ticket/22891) I'd like to
 propose a GitLab CI script for Tor Browser. My intention to be able to
 build `tor-browser-bundle` locally which I tried for some time and failed
 because of error which I hope will be brought to the attention of devs
 automatically rather than after painful reports.

 The script currently uses Ubuntu 17.04 only, but since GitLab CI is based
 on Docker images, the number of possible OS to test on is basically
 infinite.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23689>
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