fatal error: stdarg.h: No such file or directory错误的一种冷门原因

背景

最近把编译环境从Ubuntu1604 64bit升级成了Ubuntu2004 64bit，然后以前能编译的Linux驱动模块（x86，不是x64）现在突然不能编译了，提示：

whp@whp-HP-ProDesk-400-G5-MT:~/projects/F267/SVN/driver_x86/pcie_network$ make ARCH=x86
make -C ~/linux-source-4.15.0 M=/home/whp/projects/F267/SVN/driver_x86/pcie_network
make[1]: 进入目录“/home/whp/linux-source-4.15.0”
  CC [M]  /home/whp/projects/F267/SVN/driver_x86/pcie_network/fpga_dsp.o
In file included from ./include/linux/list.h:9,
                 from ./include/linux/module.h:9,
                 from /home/whp/projects/F267/SVN/driver_x86/pcie_network/fpga_dsp.c:14:
./include/linux/kernel.h:6:10: fatal error: stdarg.h: 没有那个文件或目录
    6 | #include <stdarg.h>
      |          ^~~~~~~~~~
compilation terminated.

定位解决

Makefile如下：

KDIR=~/linux-source-4.15.0
PWD=$(shell pwd)
ARCH