[RFA] sh-tdep.c (sh_use_struct_convention): Restructure and fix

[Andrew Cagney]

> 	* sh-tdep.c (sh_use_struct_convention): Clean up to have a
> 	more readable code.  Accomodate 4 byte structs with 4 byte sized
> 	first field (e.g. bitfields).

Corinna,

See: http://sources.redhat.com/ml/gdb-patches/2003-10/msg00033.html.
The ppc64_sysv_return_value code in ppc-sysv-tdep.c, has been written in 
a way that allows a quick update to this new iterface.

Andrew