i370 port

[Paul Edwards]

> You'll need to mark your new constraint as EXTRA_MEMORY_CONSTRAINT
> so that reload knows what to do when an argument doesn't match.

Thanks! That certainly produced an effect.

Unfortunately it's not quite right, seemingly not loading R9 properly:

LR    9,13
AR    9,13
MVC   0(10,9),0(2)

And it had a knock-on effect too, producing bad code elsewhere:

<          SLR   2,2
<          SLR   3,3
<          ST    2,128(13)
<          ST    3,4+128(13)
<          ST    2,136(13)
<          ST    3,4+136(13)
<          ST    2,144(13)
<          ST    3,4+144(13)
---
>          MVC   128(8,13),=F'0'
>          MVC   136(8,13),=F'0'
>          MVC   144(8,13),=F'0'

But I guess that is another can of worms to investigate.

BFN.  Paul.