[Ecls-list] Adding AO_REQUIRE_CAS before libatomic-ops include

[Daniel Herring]

On Sat, 28 Dec 2013, Christoph Egger wrote:

>  Please consider the attached patch. It enables CAS emulation on
> systems, that do not have native CAS instructions (?!), which is, for
> example, true on ARM < ARMv6

Hi Christoph,

How well is the CAS emulation working for you?

If this emulation has potential bugs or may not even compile, then it 
would probably be better to require a separate configuration flag. 
Something like --enable-cas-emulation.

Here's a snippet from the source tree that makes me think we do not want 
to set AO_REQUIRE_CAS without explicit user consent.

src/gc/libatomic_ops-1.2/doc/README.txt:
""
This emulation is slow, since it needs to disable signals. And it needs to 
block in case of contention.  If you care about performance on a platform 
that can't directly provide compare-and-swap, there are probably better 
alternatives.
""

- Daniel