[GHC] #15348: Enable two-step allocator on FreeBSD

[GHC]

#15348: Enable two-step allocator on FreeBSD
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  FreeBSD           |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4939
       Wiki Page:                    |
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Comment (by vdukhovni):

 I can try to test, but the patch is not ready yet. FreeBSD does not
 support combining `MAP_GUARD` with other flags such as `MAP_ANON` or
 `MAP_PRIVATE`, it must stand alone.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15348#comment:4>
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