[GHC] #10728: Add e.g. "-N<=4" in addition to the fixed "-N4" and variable "-N" RTS options

[GHC]

#10728: Add e.g. "-N<=4" in addition to the fixed "-N4" and variable "-N" RTS
options
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        Reporter:  rrnewton          |                Owner:  MarcelineVQ
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  7.10.2
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9221, #8224      |  Differential Rev(s):  Phab:D1650
       Wiki Page:                    |
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Comment (by thomie):

 Congratulations with your first GHC patch, Matthew.

 Still todo:
  * `-Ndiv<n>`: use the number of processors divided by <n>
  * `-Nsub<n>`: use the number of processors minus <n>
  * release notes
  * tests (use `getNumCapabilities` from `GHC.Conc.Sync`)

 Maybe you could take care of those as well?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10728#comment:11>
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