[GHC] #7790: Add dummy undefined symbols to indicate ways

[GHC]

#7790: Add dummy undefined symbols to indicate ways
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        Reporter:  ezyang            |            Owner:  ezyang
            Type:  task              |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:
      Resolution:                    |         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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Comment (by ezyang):

 This is a little more subtle: we can't add the undefined symbol at link
 step, because we want .o files to have the undefined symbols as well. And
 we need it to happen for all native code generation backends; thus, it has
 to happen before native code generation.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7790#comment:2>
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