Research: ARM threading module support

[zpl-c]

Research: ARM threading module support

[zpl-zak]

As of 10.13.x the threading module is enabled on ARMv6 and up families. Atomics currently use the standard c11 atomics library, however ideally it should be replaced by arch specific code later in the future.

Apple M1 support has been added as of 11.0.2 as well, with the same constraints as noted above.

Since C++ does not support C11 atomics library, you can't build zpl on ARM family in C++ projects, more reason to seek a way of replacing it.

[zpl-zak]

We should also consider making the atomics module optional, a good idea would be to scan and verify an internal usage of this module within ZPL itself.

If not possible, we should figure out how to ensure the atomics module operates correctly in C++ and does not depend on the C11 atomics standard library.

[zpl-zak]

Worth to look at: https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html

[zpl-zak]

11.0.11 replaces the need for c11 atomics, meaning we can use atomics in C++ on ARM now!