arm三大编译器的不同选择编译

ARM 系列目前支持三大主流的工具链，即ARM RealView (armcc), IAR EWARM (iccarm), and GNU Compiler Collection (gcc). 

   在core_cm3.h中有如下定义：

     /* define compiler specific symbols */

  #if defined ( __CC_ARM )

     #define __ASM __asm /*!< asm keyword for armcc */

     #define __INLINE __inline /*!< inline keyword for armcc */

 #elif defined ( __ICCARM__ )

     #define __ASM __asm /*!< asm keyword for iarcc */

     #define __INLINE inline /*!< inline keyword for iarcc. Only

                                   avaiable in High optimization mode! */

     #define __nop __no_operation /*!< no operation intrinsic in iarcc */

 #elif defined ( __GNUC__ )

     #define __ASM asm /*!< asm keyword for gcc */

     #define __INLINE inline /*!< inline keyword for gcc

 #endif