### Please describe the problem.

git-annex can't compile on FreeBSD; specifically, the build fails while compiling Utility.DirWatcher.Kqueue.

### What steps will reproduce the problem?

1. git clone git://git-annex.branchable.com/ git-annex
2. cd git-annex
3. stack setup
4. stack install

### What version of git-annex are you using? On what operating system?

git-annex HEAD.

FreeBSD 11.1-RELEASE r321309 GENERIC amd64

### Please provide any additional information below.

Compilation failure is as follows:

    [126 of 586] Compiling Utility.DirWatcher.Kqueue ( Utility/DirWatcher/Kqueue.hs, .stack-work/dist/x86_64-freebsd/Cabal-1.24.2.0/build/git-annex/git-annex-tmp/Utility/Di
    rWatcher/Kqueue.o )

    /usr/home/duncan/code/git-annex/Utility/DirWatcher/Kqueue.hs:112:49: error:
        Variable not in scope:
          openFd :: FilePath -> t0 -> Maybe a0 -> t1 -> IO t

    /usr/home/duncan/code/git-annex/Utility/DirWatcher/Kqueue.hs:112:60: error:
        Data constructor not in scope: ReadOnly

    /usr/home/duncan/code/git-annex/Utility/DirWatcher/Kqueue.hs:112:77: error:
        Variable not in scope: defaultFileFlags

    /usr/home/duncan/code/git-annex/Utility/DirWatcher/Kqueue.hs:132:15: error:
        Variable not in scope: closeFd :: Fd -> IO b0

    /usr/home/duncan/code/git-annex/Utility/DirWatcher/Kqueue.hs:170:14: error:
        Variable not in scope: closeFd :: Fd -> IO ()
    Completed 210 action(s).

    --  While building custom Setup.hs for package git-annex-6.20180807 using:
          /usr/home/duncan/code/git-annex/.stack-work/dist/x86_64-freebsd/Cabal-1.24.2.0/setup/setup --builddir=.stack-work/dist/x86_64-freebsd/Cabal-1.24.2.0 build exe:git
    -annex --ghc-options " -ddump-hi -ddump-to-file"
        Process exited with code: ExitFailure 1

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Not yet.  But I'm used to issues compiling new tools on FreeBSD, so I'm in no way disheartened by this :)

> [[done]] --[[Joey]]
