Adds initial ThreadX support through a SpinLock backend for
pw_sync. Note that this first backend does not support ThreadX
with SMP enabled, taking a shortcut to detect SpinLock recursion
instead.
Change-Id: I6cb4d1edfe78bc97fc632cfb353589e53f87f2c7
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/25803
Commit-Queue: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
