[C++] Add WEAK for cplusplus_system_init routine.

components/cplusplus/crt_init.c

@@ -22,6 +22,7 @@
 * 2014-12-03     Bernard      Add copyright header.
 * 2014-12-29     Bernard      Add cplusplus initialization for ARMCC.
 * 2016-06-28     Bernard      Add _init/_fini routines for GCC.
+* 2016-10-02     Bernard      Add WEAK for cplusplus_system_init routine.
 */
 
 #include <rtthread.h>
@@ -44,22 +45,18 @@ void _fini()
 }
 #endif
 
+WEAK
 int cplusplus_system_init(void)
 {
 #if defined(__GNUC__) && !defined(__CC_ARM)
-    extern unsigned char __ctors_start__;
-    extern unsigned char __ctors_end__;
-    typedef void (*func)(void);
+    typedef void (*pfunc) ();
+    extern pfunc __ctors_start__[];
+    extern pfunc __ctors_end__[];
+    pfunc *p;
 
-    /* .ctors initalization */
-    func *ctors_func;
+    for (p = __ctors_start__; p < __ctors_end__; p++)
+        (*p)();
 
-    for (ctors_func = (func *)&__ctors_start__;
-         ctors_func < (func *)&__ctors_end__;
-         ctors_func ++)
-    {
-        (*ctors_func)();
-    }
 #elif defined(__CC_ARM)
     /* If there is no SHT$$INIT_ARRAY, calling
      * $Super$$__cpp_initialize__aeabi_() will cause fault. At least until Keil5.12