CMake: Link static libstdc++ and gcc for exes

This way stuff will work without having to tote around a manual copy of
mingw's libraries

Change-Id: Ie80b742f2e10960acdddb8a2339dc64704dc43fc
Reviewed-on: http://review.couchbase.org/33332
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>