[cairo] pixman - building error on Linux

[cu]

This is the error I get when building pixman-0.18.2 on Ubuntu. This does
not seem to affect the actual library, which is still usable. However, I
can't find referenced functions in pixman source either.

CCLD   clip-test
clip-test.o: In function `main':
clip-test.c:(.text+0x1bf): undefined reference to
`pixman_region32_init_rect'
clip-test.c:(.text+0x1cb): undefined reference to
`pixman_image_set_clip_region32'

Ideas welcome.