zephyr: rtos: Allow memory operations to be called from cpp code

The memcpy_s() function is called from CPP code in IADK modules.
Declare it as extern "C" when header included in CPP code.

Signed-off-by: Jaroslaw Stelter <Jaroslaw.Stelter@intel.com>

zephyr/include/rtos/string.h

@@ -11,6 +11,9 @@
 #include <stddef.h>
 #include <errno.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 /* missing from zephyr - TODO: convert to memset() */
 #define bzero(ptr, size) \
 	memset(ptr, 0, size)
@@ -60,4 +63,8 @@ static inline int memset_s(void *dest, size_t dest_size, int data, size_t count)
 	return 0;
 }
 
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
 #endif /* __ZEPHYR_RTOS_STRING_H__ */