[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
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  ​Phab:D1988
       Wiki Page:                    |
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Comment (by Erik de Castro Lopo <erikd@…>):

 In [changeset:"46f9a476e17714e27d893b491cc0dcf68c745249/ghc" 46f9a47/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="46f9a476e17714e27d893b491cc0dcf68c745249"
 DriverPipeline: Fix 'unused arguments' warnings from Clang

 When using Clang as the C compiler, over 100 tests were failing
 due to Clang reporting that some command line arguments were not
 being used. These warnings only occur when Clang is compiling
 assembler files which happens in two places, one of which already
 conditionally adding `-Qunused-arguments` to the command line when
 the compiler was Clang. This fixes the other.

 Test Plan: validate with clang as the C compiler

 Reviewers: bgamari, hvr, austin, rwbarton

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1998

 GHC Trac Issues: #11684
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11684#comment:12>
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