[polyml] Sparc support

There's been a problem with the multiprocessor code in Poly/ML on the Sparc and I've traced this to some hand-coded assembly code. The problem is that v9 processors appear to require memory barrier instructions in the atomic increment and decrement instructions but these instructions aren't implemented on earlier processors. That really means that there have to be different versions of the code for v9 and for earlier processors.

There are various options for dealing with this requiring more or less effort but I'd first like to have some idea of how much Sparc machines are currently used. If they are used are these v9 processors or are people still using v8/v7 processors?

David