[GHC] #13375: ghc-pkg "cache is out of date" message breaks testsuite

[GHC]

#13375: ghc-pkg "cache is out of date" message breaks testsuite
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.2.1
          Component:  ghc-pkg        |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Since the merge of the package database locking business, `ghc-pkg dump`
 spews a message on `stderr` on Windows,
 {{{
 $ "C:/msys64/home/ben/ghc/inplace/bin/ghc-pkg.exe" dump
 WARNING: cache is out of date:
 C:\msys64\home\ben\ghc\inplace\lib\package.conf.d\package.cache
 ghc will see an old view of this package db. Use 'ghc-pkg recache' to fix.
 name: xhtml
 version: 3000.2.1
 id: xhtml-3000.2.1
 ...
 }}}

 When the testsuite driver sees this it (namely `testutil.getStdout`)
 assumes something has gone terribly wrong and aborts.

 From a cursory look it's not clear how we got into this situation; the
 file indeed exists and was certainly touched during the build. However,
 running `ghc-pkg recache` indeed seems to fix the issue.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13375>
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