move misc/speculation.h to sys/speculation.h and
create a shim for backward-compatibility.
No functional changes to the headers.
A warning in the shim can be controlled with CONFIG_COMPAT_INCLUDES.
Related to #16539
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
Used to sanitize array indexes without using any branch
instructions. Should be portable to any architecture.
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
