sh4 abi doc

[Andrew Cagney]

> "When an aggregate type is returned in R0 and R1, R0 contains the first
> four bytes of the aggregate, and R1 contains the remainder. If the size
> of the aggregate type is not a multiple of 4 bytes, the aggregate is
> tail-padded up to a multiple of 4 bytes. The value of the padding is
> undefined.

Suggest clarifying this.  In particular how tail ``tail-padding'' 
interacts with LE and BE.  I think I know what this means (having seen 
the MIPS) but (having seen the MIPS) I also know how badly it can be 
botched :-(

enjoy,
Andrew