错误提示:
c:/keil_v5/arm/gcc/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld.exe: c:/keil_v5/arm/gcc/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp\libc_nano.a(lib_a-init.o): in function `__libc_init_array':
init.c:.text.__libc_init_array+0x12): undefined reference to `_init'