[GHC] #12624: Un-revert PosixSource.h cleanup

[GHC]

#12624: Un-revert PosixSource.h cleanup
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2579
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"8dc72f3c33b0e724ddb690c9d494969980c10afd/ghc"
 8dc72f3c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8dc72f3c33b0e724ddb690c9d494969980c10afd"
 Cleanup PosixSource.h

 When trying to build arm64-apple-iso, the build fell over `strdup`, as
 the arm64-apple-ios build did not fall into `darwin_HOST_OS`, and would
 need `ios_HOST_OS`.

 This diff tries to clean up PosixSource.h, instead of layering another
 define on top.

 As we use `strnlen` in sources that include PosixSource.h, and `strnlen`
 is defined in POSIX.1-2008, the `_POSIX_C_SOURCE` and `_XOPEN_SOURCE`
 are increased accordingly.

 Furthermore the `_DARWIN_C_SOURCE` (required for `u_char`, etc. used in
 sysctl.h) define is moved into `OSThreads.h` alongside a similar ifdef
 for freebsd.

 Test Plan: Build on all supported platforms.

 Reviewers: austin, simonmar, erikd, kgardas, bgamari

 Reviewed By: simonmar, erikd, kgardas, bgamari

 Subscribers: Phyx, hvr, thomie

 Differential Revision: https://phabricator.haskell.org/D2579

 GHC Trac Issues: #12624
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12624#comment:10>
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