The source project of this merge request has been removed.
Call cairo.get_include() to find py3cairo.h
If pycairo was installed from source, py3cairo.h may not have been copied to /usr/include/pycairo. It would be better to ask the pycairo module itself where py3cairo.h is by calling cairo.get_include().
This fixes compilation on CentOS 7 when pycairo has been installed from source.