Stack variables

[amylaar@cygnus.co.uk]

> It's an interesting thought, but separating the stack variables from
> other uses of the stack might be rather difficult.  There's also significant
> code in the compiler which knows special things about the stack or frame
> poiner (look for stack_pointer_rtx in reload*.c and many other files).

Well, what we could do without rewriting significant parts of the compiler
would be to add two extra stack pages in the prologue, and unmap a properly
aligned page in that area.  The epilogue would then have to clean this up.
This should be possible even in a machine description, so no backend
patches would be needed.