add ci build for all at32, use linker and startup from mcu cmsis instead of local files

examples/build_system/make/cpu/cortex-m4-nofpu.mk

@@ -0,0 +1,20 @@
+ifeq ($(TOOLCHAIN),gcc)
+  CFLAGS += \
+    -mthumb \
+    -mcpu=cortex-m4 \
+    -mfloat-abi=soft
+
+else ifeq ($(TOOLCHAIN),clang)
+  CFLAGS += \
+	  --target=arm-none-eabi \
+	  -mcpu=cortex-m4
+
+else ifeq ($(TOOLCHAIN),iar)
+  CFLAGS += --cpu cortex-m4 --fpu none
+  ASFLAGS += --cpu cortex-m4 --fpu none
+
+else
+  $(error "TOOLCHAIN is not supported")
+endif
+
+FREERTOS_PORTABLE_SRC ?= $(FREERTOS_PORTABLE_PATH)/ARM_CM3