[GHC] #13138: Clean up ghc-pkg validation warnings in build log

[GHC]

#13138: Clean up ghc-pkg validation warnings in build log
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        Reporter:  mpickering        |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 That's a good question. You can easily see it still happens by looking at
 the `stderr` of any GHC build  (for example,
 https://phabricator.haskell.org/harbormaster/build/25271/?l=0). The reason
 why I haven't been able to fix this yet (with D3322) is that these entries
 don't appear in my local build logs when running `./validate`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13138#comment:2>
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