target-sparc: fix 32bit integer division overflow

The signed integer division -0x8000_0000_0000_0000 / -1 must be handled
separately to avoid an overflow on the QEMU host.

Negative overflow must be a negative number for correct sign
extension in Sparc64 mode. Use <stdint.h> constants.

Signed-off-by: Olivier Danet <odanet@caramail.com>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
