add ci build for at32: f402_405, f403a_407, f423

hw/bsp/at32f425/family.c

@@ -282,11 +282,15 @@ size_t board_get_unique_id(uint8_t id[], size_t max_len)
   }
 #endif
 
-void HardFault_Handler(void)
-{
+void HardFault_Handler(void) {
   __asm("BKPT #0\n");
 }
 
+// Required by __libc_init_array in startup code if we are compiling using
+// -nostdlib/-nostartfiles.
+void _init(void) {
+}
+
 #ifdef  USE_FULL_ASSERT
 void assert_failed(const char *file, uint32_t line)
 {

hw/bsp/at32f425/family.mk

@@ -15,7 +15,7 @@ CFLAGS += \
 	-DCFG_TUSB_MCU=OPT_MCU_AT32F425 \
 
 LDFLAGS_GCC += \
-	-flto --specs=nosys.specs
+	-flto --specs=nosys.specs -nostdlib -nostartfiles
 
 SRC_C += \
 	src/portable/synopsys/dwc2/dcd_dwc2.c \