sh: Export div symbols for GCC 4.2 and ST GCC.

GCC 4.2 can emit integer variants of the FP division routines, so
these need to be exported in order to keep the modules happy.

4.1.x versions of the ST compiler have these things backported,
and so also generate these symbols (whereas vanilla gcc 4.1.x
does not), so handle the __GNUC_STM_RELEASE__ case to accomodate
updated versions of the 4.1.x toolchain.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>