1.add can and on-chip-flash drivers 2.fixed c++ compiler error

Author: sheltonyu

bsp/at32/Libraries/AT32_Std_Driver/AT32F4xx_StdPeriph_Driver/inc/at32f4xx_ertc.h

@@ -11,6 +11,9 @@
 #ifndef __AT32F4xx_ERTC_H
 #define __AT32F4xx_ERTC_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /* Includes ------------------------------------------------------------------*/
 #include "at32f4xx.h"

bsp/at32/Libraries/rt_drivers/SConscript

@@ -43,9 +43,15 @@ if GetDepend('BSP_USING_SRAM'):
 if GetDepend('BSP_USING_RTC'):
     src += ['drv_rtc.c']
 
+if GetDepend('BSP_USING_ON_CHIP_FLASH'):
+    src += ['drv_flash.c']
+
 if GetDepend(['BSP_USING_WDT']):
     src += ['drv_wdt.c']
 
+if GetDepend(['BSP_USING_CAN']):
+    src += ['drv_can.c']
+
 if GetDepend(['BSP_USING_SDIO']):
     src += ['drv_sdio.c']