add system() for IAR

Author: mysterywolf

components/libc/compilers/dlib/syscalls.c

@@ -6,6 +6,7 @@
  * Change Logs:
  * Date           Author       Notes
  * 2021-02-13     Meco Man     implement exit() and abort()
+ * 2021-02-20     Meco Man     add system()
  */
 #include <rtthread.h>
 
@@ -16,3 +17,9 @@ void __exit (int status)
     __rt_libc_exit(status);
     while(1);
 }
+
+int system(const char * string)
+{
+    extern int __rt_libc_system(const char *string);
+    return __rt_libc_system(string);
+}