[GHC] #2123: implement waitForProcess using signals

[GHC]

#2123: implement waitForProcess using signals
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 Reporter:  simonmar           |          Owner:                  
     Type:  task               |         Status:  new             
 Priority:  normal             |      Milestone:  6.10 branch     
Component:  libraries/process  |        Version:  6.8.2           
 Severity:  normal             |     Resolution:                  
 Keywords:                     |     Difficulty:  Moderate (1 day)
 Testcase:                     |   Architecture:  Unknown         
       Os:  Unknown            |  
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Comment (by duncan):

 The other advantage is that `ProcessHandle`s become safe to discard/forget
 without ending up with defunct zombie processes under Unix.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2123#comment:1>
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