代码拉取完成，页面将自动刷新
【问题描述】
在Ubuntu18.04上编译报如下错误
make[1]: Leaving directory '/home/wen_fei/qemu/qemu/slirp'
CHK version_gen.h
GEN docs/version.texi
SPHINX docs/built/interop
SPHINX docs/built/devel
SPHINX docs/built/interop
SPHINX docs/built/specs
GEN qemu-doc.txt
GEN docs/interop/qemu-qmp-ref.txt
GEN docs/interop/qemu-qmp-ref.html
GEN qemu-doc.html
CC block.o
GEN docs/interop/qemu-ga-ref.html
GEN docs/interop/qemu-ga-ref.txt
Warning, treated as error:
Invalid configuration value found: 'language = None'. Update your configuration to a valid language code. Falling back to 'en' (English).
GEN arm-linux-user/config-target.h
Makefile:994: recipe for target 'docs/built/devel/index.html' failed
make: *** [docs/built/devel/index.html] Error 2
make: *** Waiting for unfinished jobs....
Warning, treated as error:
Invalid configuration value found: 'language = None'. Update your configuration to a valid language code. Falling back to 'en' (English).
Warning, treated as error:
Invalid configuration value found: 'language = None'. Update your configuration to a valid language code. Falling back to 'en' (English).
【问题分析】
该问题是因为Sphinx工具的一个bug，在部分版本中会出现告警，因此避免该告警的方法就是直接将language设置为'en'即可
