[STM32F4xx-HAL] Fix link error when enable cmbacktrace package.

Change-Id: I879acd7c67ea782389b8f69acb2846c2879f8fcf

bsp/stm32f4xx-HAL/stm32_rom.ld

@@ -80,6 +80,7 @@ SECTIONS
 
     .stack : 
     {
+        _sstack = .;
         . = . + _system_stack_size;
         . = ALIGN(4);
         _estack = .;