CppunitTest_sw_ooxmlfieldexport: enable on OS X

Change-Id: I3ded4fc864870c20e0e5a7dc0aef02ca7b792ebc
Reviewed-on: https://gerrit.libreoffice.org/10372
Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>