More real.c fall out - XFmode real_format_for_mode[] entry not initialised before use.

[Graham Stott]

Richard,

Ignore what I wrote I got lost in the initialisation code.

It's a m68k backend problem which has multiple definitions of OVERRIDE_OPTIONS.
The OVERRIDE_OPTIONS define in m68kelf.h doesn't call override_options which
means that the initailisation of real_format_for_mode isn't being done for
m68k-elf target.

Graham