* Add link dependency on xproto to xau
The libxcb build was failing like so:
```
1 error found in build log:
[ ... ]
131 checking whether to build developer documentation... yes
132 checking for doxygen... /usr/bin/doxygen
133 checking for dot... /usr/bin/dot
134 checking for CHECK... no
135 checking for XCBPROTO... yes
136 checking for NEEDED... no
>> 137 configure: error: Package requirements (pthread-stubs xau >= 0.99.2) were not met:
138
139 Package 'xproto', required by 'xau', not found
140
141 Consider adjusting the PKG_CONFIG_PATH environment variable if you
142 installed software in a non-standard prefix.
143
```
This adds a link dependency on libxproto that allows the libxcb build to
succeed.
* Change more build deps to build, link
These were also necessary for emacs+X to build.
* Fix flake8 complaint
b9d7903cdb