Blackfin: fix miscompilation in lshrdi3

The code used in the Blackfin lshrdi3 utilizes gcc constructs.  However,
the structures declared don't line up with the code gcc generates, so
under certain optimizations, we get bad code and things crap out in fun
random ways.  So rather than trying to maintain different gcc definitions
ourselves, just use the ones available in gcclib.h.

URL: http://blackfin.uclinux.org/gf/tracker/5286
Signed-off-by: Jie Zhang <jie.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>