[GHC] #11684: Fix tests with Clang

[GHC]

#11684: Fix tests with Clang
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           Reporter:  erikd          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Configuring GHC with `--with-gcc=clang` and then running the tests
 currently causes over 100 test failues. The vast majority are due to
 stderr differences due to Clang producing more warnings, specifically
 `warning: argument unused during compilation`.

 The obvious solution would be to filter these out in the testsuite runner.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11684>
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