[GHC] #13111: maintainer-clean should clean build.mk

[GHC]

#13111: maintainer-clean should clean build.mk
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           Reporter:  bgamari        |             Owner:
               Type:  task           |            Status:  new
           Priority:  highest        |         Milestone:  8.2.1
          Component:  Build System   |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Unfortunately `maintainer-clean` doesn't clean `mk/build.mk`, which lead
 to bad binary distributions being distributed for 8.0.2. This needs to be
 fixed.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13111>
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