这里显示一个错误信息：
checking for LIBXML2… configure: error: Package requirements (libxml-2.0 >=
2.6) were not met:
No package ‘libxml-2.0′ found
Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.
Alternatively, you may set the environment variables LIBXML2_CFLAGS
and LIBXML2_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
但是我们在上面其实已经安装上 libxml2 了的，这里只是一个 环境变量没有设置好而已。
解决办法： 确定 /usr/local/libxml2/lib/pkgconfig 目录下有 libxml-2.0.pc
export PKG_CONFIG_PATH=/usr/local/libxml2/lib/pkgconfig:$PKG_CONFIG_PATH
再次生成 makefile , 这样就成功了