rm48x50: restore missing include for __TI_COMPILER_VERSION__

include/rtdef.h

@@ -161,6 +161,7 @@ typedef rt_base_t                       rt_off_t;       /**< Type for offset */
     #define rt_inline                   static __inline
     #define RTT_API
 #elif defined (__TI_COMPILER_VERSION__)
+    #include <stdarg.h>
     /* The way that TI compiler set section is different from other(at least
      * GCC and MDK) compilers. See ARM Optimizing C/C++ Compiler 5.9.3 for more
      * details. */