[GHC] #14375: Implement with# primop

[GHC]

#14375: Implement with# primop
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        Reporter:  simonpj           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14346            |  Differential Rev(s):  ​Phab:D4110,
       Wiki Page:                    |  Phab:D4189
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Comment (by bgamari):

 Merged to `ghc-8.6` and `master`. Hopefully we will be able to revert this
 when `with#` is merged in (likely) 8.8.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14375#comment:15>
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