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 <erwin@erwinrol.com>

include/sys/__assert.h

@@ -80,9 +80,19 @@
 #endif
 
 #if __ASSERT_ON
+
 #include <sys/printk.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 void assert_post_action(const char *file, unsigned int line);
 
+#ifdef __cplusplus
+}
+#endif
+
 #define __ASSERT_LOC(test)                               \
 	printk("ASSERTION FAIL [%s] @ %s:%d\n",    \
 	       Z_STRINGIFY(test),                         \