[GHC] #8787: compiler/ghc.mk: restore GhcHcOpts variable handling

[GHC]

#8787: compiler/ghc.mk: restore GhcHcOpts variable handling
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       Reporter:  slyfox            |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 wiki and mk/config.mk.in suggests setting GhcHcOpts
 for compiler-wide haskell flags. But it does not
 work for a while now.

 Proposed patch fixes it.

 Thanks!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8787>
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