linux上编译程序时由于arm-none-eabi-gcc版本过老出现警告
一.问题描述：
当使用make进行程序编译的时候出现如下警告，原因是用于编译的arm-none-eabi版本过老的缘故
nickcong@nickcong-Inspiron-3537:~/crazyflie-firmware$ sudo makeCLEAN_VERSION
VTMPL version.c
CC version.o
LD cf2.elf
/usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/bin/ld: warning: /usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/lib/armv7e-m/fpu/libc_nano.a(lib_a-atexit.o) uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail
/usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/bin/ld: warning: /usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/lib/armv7e-m/fpu/libc_nano.a(lib_a-ctype_.o) uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail
/usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/bin/ld: warning: /usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/lib/armv7e-m/fpu/libc_nano.a(lib_a-errno.o) uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail
/usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/bin/ld: warning: /usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/lib/armv7e-m/fpu/libc_nano.a(lib_a-__call_atexit.o) uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail
COPY cf2.hex
COPY cf2.bin
DFUse cf2.dfu
Crazyflie 2.0 build!
Build 43:a626925d4b07 (2017.06-43) MODIFIED
Version extracted from git
Crazyloader build!
text data bss dec hex filename
139808 2592 63240 205640 32348 cf2.elf
虽然程序能顺利编译通过，但是对于有一点强迫症的我来说，还是不舒服，根据论坛的办法去解决但是总是有点问题
下面记录一下每一步的解决过程与碰到的问题
1.如果直接在终端上
sudo apt-get install gcc-arm-none-eabi
则在repo服务器上下载的还是4.9.3，不是官网上最新的
二.试错过程
后面决定直接在
GNU Arm Embedded Toolchain上下载，网址：下载链接
按照网上的办法下载下来解压后，添加环境变量后还是有警告
仔细看一遍警告
2.1分析
warning: /usr/lib/gcc/arm-none-eabi/4.9.3/../../../arm-none-eabi/lib/armv7e-m/fpu/libc_nano.a(lib_a-strncmp.o) uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail
它一直使用的是 /usr/lib/gcc下的/arm-none-eabi/4.9.3
当我键入which arm-none-eabi-gcc显示
/usr/bin/gcc-arm-none-eabi-7-2017-q4-major/bin//arm-none-eabi-gcc
因此后面手动把
/usr/lib/gcc下的/arm-none-eabi/4.9.3给删除了，事实证明我是手贱，在一次编译的时候直接报错，后面
幸亏依靠新立得才重新还原了回去，
虽然还是有警告，但是总比报错好
三、最后的解决办法：
最后的问题是出在Makefile上，在Makefile里CROSS_COMPILE ?=arm-none-eabi-，它可能是使用默认路径，因此需要
把编译的路径修改一下，最后修改为CROSS_COMPILE ?= /home/nickcong/gun_tools_2017/gcc-arm-none-eabi-7-2017-q4-major/bin/arm-none-eabi-
大功告成！
解决的思路来自于思路链接