toolchain: Add global check for endianness preprocessor definitions.

This commit adds a global check for __BYTE_ORDER__,
__ORDER_LITTLE_ENDIAN__ and __ORDER_BIG_ENDIAN__ preprocessor
definitions that are used throughout the Zephyr codebase.

These preprocessor definitions being not defined can easily
go unnoticed and cause unexpected behaviours, as detailed in
PR #18922.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>