[GHC] #13412: Centralize the definition for GHC's libdir on Windows

[GHC]

#13412: Centralize the definition for GHC's libdir on Windows
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           Reporter:  Elieux            |             Owner:  (none)
               Type:  task              |            Status:  new
           Priority:  low               |         Milestone:
          Component:  None              |           Version:  8.0.2
           Keywords:                    |  Operating System:  Windows
       Architecture:  Unknown/Multiple  |   Type of failure:  Other
          Test Case:                    |        Blocked By:
           Blocking:                    |   Related Tickets:
Differential Rev(s):                    |         Wiki Page:
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 The location of GHC libraries on Windows is currently something like
 `$bindir/../lib` (because the whole distribution can be put anywhere on
 the filesystem, there are no absolute paths), but this information is
 hard-coded in multiple places instead of being defined in one place. To be
 clear, I mean only the relative path (`../lib`); the base still needs to
 be determined at runtime.

 I assume that tools that can rely on `ghc --info` (or equivalent) already
 do that. If there are any that don't, they should be fixed regardless. The
 build system, ghc, ghc-cabal, ghc-pkg, hsc2hs, haddock... should all be
 able to get the relative path from `configure`'s output.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13412>
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