Add the lacked definitions to mbed_rtx.h

I added the below definitions for working "Dynamic Stack" and "Dynamic heap" on Mbed OS by referencing with the codes of Cortex-M target board.
"ISR_STACK_START", "ISR_STACK_SIZE", "INITIAL_SP", "HEAP_START" and "HEAP_SIZE"

Author: TomoYamanaka

targets/TARGET_RENESAS/mbed_rtx.h

@@ -16,4 +16,32 @@
 #ifndef MBED_MBED_RTX_H
 #define MBED_MBED_RTX_H
 
-#endif  // MBED_MBED_RTX_H
+#include <stdint.h>
+
+#define OS_IDLE_THREAD_STACK_SIZE   512
+
+#if defined(__CC_ARM)
+    extern char Image$$ARM_LIB_STACK$$Base[];
+    extern char Image$$ARM_LIB_STACK$$ZI$$Limit[];
+    extern char Image$$ARM_LIB_HEAP$$Base[];
+    #define ISR_STACK_START       ((unsigned char*)Image$$ARM_LIB_STACK$$Base)
+    #define ISR_STACK_SIZE        ((uint32_t)((uint32_t)Image$$ARM_LIB_STACK$$ZI$$Limit - (uint32_t)Image$$ARM_LIB_STACK$$Base))
+    #define INITIAL_SP            (Image$$ARM_LIB_STACK$$ZI$$Limit)
+    #define HEAP_START            ((unsigned char*)Image$$ARM_LIB_HEAP$$Base)
+    #define HEAP_SIZE             ((uint32_t)((uint32_t)ISR_STACK_START - (uint32_t)HEAP_START))
+#elif defined(__GNUC__)
+    extern uint32_t               __StackTop;
+    extern uint32_t               __StackLimit;
+    extern uint32_t               __end__;
+    #define ISR_STACK_START       ((unsigned char*)&__StackLimit)
+    #define ISR_STACK_SIZE        ((uint32_t)((uint32_t)&__StackTop - (uint32_t)&__StackLimit))
+    #define INITIAL_SP            (&__StackTop)
+    #define HEAP_START            ((unsigned char*)&__end__)
+    #define HEAP_SIZE             ((uint32_t)((uint32_t)ISR_STACK_START - (uint32_t)HEAP_START))
+#elif defined(__ICCARM__)
+    /* No region declarations needed */
+#else
+    #error "no toolchain defined"
+#endif
+
+#endif  // MBED_MBED_RTX_H