Build pixman internally as a private part of cairo, with suitable name changes to avoid any visible pixman symbols in the cairo library:
Descend into pixman.
Drop libpixman from Requires.
Don't check for libpixman. Check version of pkg-config and use Requires.private instead of Requires in cairo.pc if possible. Generate pixman Makefiles.
Rip out release-publish target and installation of libpixman.pc.
Add pixman-remap.h. Drop libpixman.la target.
Fix to include config.h rather than ../config.h
This is the cpp magic to rename all pixman functions from the various fb, Fb, INT_pixman, pixman, Render, _Render, or no prefix to _cairo_pixman_ prefixes.
Include pixman-remap.h to get all the cairo-internalized names.
Add -Ipixman/src to get at pixman-remap.h.