sys/__assert.h: Fix __assert.h so it can be included in C++ code
sys/__assert.h: Fix __assert.h so it can be included in C++ code

Add extern "C" to __assert.h so it can be included into C++ code.

Signed-off-by: Erwin Rol <0c2a6e12a3ee3123563f88831cd6d692c33fb195@erwinrol.com>

finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr