bug#24892: {s, }brk removed from FreeBSD 11.x and later, arm64 architecture

[Paul Eggert <eggert@cs.ucla.edu>]

On 11/09/2016 04:22 PM, Richard Stallman wrote:
> The point of memory-limit was to enable features useful for users.
> If memory-limit doesn't work any more, those features don't either.
>
> What exactly were those features?  What problems did they help
> users deal with?
I assume memory-limit was an attempt to let Lisp code diagnose when 
memory was getting low in Emacs, circa 1992. The memory-limit function 
was added in commit 20d2471455526acfd5fe96681ea31f0eac88fae4 by Jim 
Blandy on 1992-10-03. As far as I can see the function was never 
successful, in the sense that this part of the code was being developed 
at the time and that Emacs eventually used other methods (e.g., calls 
from C to sbrk (0)) to get the information that memory-limit was returning.
> Are they completely unnecessary now?  If not, can we make them
> function again?  Or provide other features to deal with the same
> problems?

This particular feature, whatever it was, seems to have become 
unnecessary in late 1992, soon after it was added.