Also set SHARED_LINKER_FLAGS for -static-libgcc

Avoids having to port libgcc to windows for simple runs

Change-Id: Ibc3345097965965ecd531b4fe41703bac9539418
Reviewed-on: http://review.couchbase.org/35874
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>