bug#30248: Can't build Emacs pretest 26.0.91

[martin rudalics]

> Last Emacs built successfully from source here is
> GNU Emacs 25.1.91.1 (i686-pc-linux-gnu, GTK+ Version 3.14.5) of 2017-01-02
[...]
> /usr/lib/gcc/i586-linux-gnu/4.9/../../../i386-linux-gnu/libgdk-3.so: 
undefined reference to `cairo_surface_set_device_scale'
> /usr/lib/gcc/i586-linux-gnu/4.9/../../../i386-linux-gnu/libgtk-3.so: 
undefined reference to `cairo_surface_get_device_scale'

This indicates that the gdk and cairo libraries found by the build
script mismatch.  You may have to either downgrade gtk, upgrade cairo,
or make sure that nothing shadows cairo in the load path.

And please tell us the options used when configuring Emacs.

Thank you, martin