错误“checking build system type... config.sub: missing argument”的解决办法

背景：交叉编译avahi库时遇到错误“checking build system type... config.sub: missing argument” ,“configure:error: /bin/bash ./config.sub failed” ，如下图：

编译脚本：

#! /bin/bash
<<'COMMENT'
@File    :   avahi-compile.sh
@Time    :   2019/05/30 19:27:09
@Author  :   LiPingping 
@Version :   1.0
@Contact :   youmakemewhole@163.com
@License :   (C)Copyright 2017-2018, Twirling in time
@Desc    :   None
COMMENT

# here is main shell code.
export CPPFLAGS="-I/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/expat/include"
export CFLAGS="-I/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/expat/include"
export LDFLAGS="-L/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/expat/lib" 

./configure --host=aarch64-linux-gnu \
    --prefix=$(pwd)/../build_out/avahi \
    --with-distro=archlinux \
    --localstatedir=/var \
    --with-xml=expat \
    --with-avahi-user=root \ 
    --with-avahi-group=root \
    --disable-gdbm --disable-qt3 --disable-qt4 --disable-qt5  --disable-gtk --disable-gtk3 --disable-python --disable-mono --disable-pygobject \
    --disable-doxygen  --disable-manpages  --disable-libevent --disable-FEATURE --disable-glib --disable-gobject \
    DBUS_CFLAGS="-I/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/dbus/include/dbus-1.0/ -I/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/dbus/lib/dbus-1.0/include/" \
    DBUS_LIBS="-L/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/dbus/lib -ldbus-1" \
    LIBDAEMON_CFLAGS="-I/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/daemon_arm_prefix/include" \
    LIBDAEMON_LIBS="-L/home/lee/Desktop/twProject/snapcast/snapcast-rockship/Nenopi2-cross-compile-libs/build_out/daemon_arm_prefix/lib -ldaemon"

解决办法：

查找资料后，首先，我确认config.sub有可执行权限，其次，排查空格问题，最后找到在“--with-avahi-user=root \ ”的“\ ”后面找到一个空格，去掉\后的空格即可。解决办法让人意想不到。

参考：

Steps to cross-compile "avahi".

http://www.linuxdiyf.com/linux/22364.html

https://www.cnblogs.com/pysery/archive/2012/06/17/2552680.html