Bug#874077: clutter-1.0: build tests fail on Debian but pass on Ubuntu

[Jeremy Bicha]

Control: reassign src:xorg-server 2:1.20.1-1
Control: affects -1 src:clutter-1.0

I have an easier test case: libepoxy (since it builds a lot faster
than clutter) [1]. The tests pass if I change the dh_auto_test
override to

xvfb-run -s "-screen 0 640x480x16" dh_auto_test

Therefore, it looks like Debian needs to grab this commit:

https://salsa.debian.org/xorg-team/xserver/xorg-server/commit/ec812c8f74b4f

[1] https://salsa.debian.org/debian/libepoxy

Thanks,
Jeremy Bicha