These are macros that are expected to be defined at all times by
the compiler. We need them at the very beginning of kernel.h for
the k_thread definition, before it's possible to include arch.h.
Make a special toolchain header for XCC compiler and place these
defines in there. Otherwise inherit all the other GCC defines.
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
