CMSIS/RTX: Move Idle and Timer thread stack to bss section.

In case of ARM compiler, idle and timer thread stack though assigned
to `.bss.os` section since not zero initialized are part of `data` section.

In this commit, we are moving stacks of idle and timer thread to bss
section and thereby saving ROM space.

Author: deepikabhavnani

rtos/source/TARGET_CORTEX/rtx5/RTX/Source/rtx_lib.c

@@ -125,9 +125,12 @@ static osRtxThread_t os_idle_thread_cb \
 __attribute__((section(".bss.os.thread.cb")));
 
 // Idle Thread Stack
+#if defined (__CC_ARM)
+static uint64_t os_idle_thread_stack[OS_IDLE_THREAD_STACK_SIZE/8];
+#else
 static uint64_t os_idle_thread_stack[OS_IDLE_THREAD_STACK_SIZE/8] \
 __attribute__((section(".bss.os.thread.stack")));
-
+#endif
 // Idle Thread Attributes
 static const osThreadAttr_t os_idle_thread_attr = {
 #if defined(OS_IDLE_THREAD_NAME)
@@ -181,9 +184,13 @@ __attribute__((section(".data.os.timer.mpi"))) =
 static osRtxThread_t os_timer_thread_cb \
 __attribute__((section(".bss.os.thread.cb")));
 
+#if defined (__CC_ARM)
+static uint64_t os_timer_thread_stack[OS_TIMER_THREAD_STACK_SIZE/8];
+#else
 // Timer Thread Stack
 static uint64_t os_timer_thread_stack[OS_TIMER_THREAD_STACK_SIZE/8] \
 __attribute__((section(".bss.os.thread.stack")));
+#endif
 
 // Timer Thread Attributes
 static const osThreadAttr_t os_timer_thread_attr = {