s390: Use long branches across object boundaries (jgh instead of jh)

Depending on the layout chosen by the linker, the 16-bit displacement
of the jh instruction is insufficient to reach the target label.

Analysis of the linker failure was carried out by Nick Clifton.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Stefan Liebler <stli@linux.ibm.com>