fix app start

Author: Jan Kamidra

targets/TARGET_STM/TARGET_STM32U0/TARGET_STM32U083xC/TOOLCHAIN_GCC_ARM/startup_stm32u083xx.s

@@ -93,8 +93,9 @@ LoopFillZerobss:
 
 /* Call static constructors */
   bl __libc_init_array
+  
 /* Call the application's entry point.*/
-  bl main
+  bl _start
 
 LoopForever:
   b LoopForever

targets/targets.json5

@@ -4767,8 +4767,7 @@ mode is recommended for target MCUs with small amounts of flash and RAM.",
             "STM32U0"
         ],
         "macros_add": [
-            "MBED_TICKLESS",
-            "EXTRA_IDLE_STACK_REQUIRED"
+            "MBED_TICKLESS"
         ],
         "config": {
             "clock_source": {