Ok, so I ran into a problem because rusage.h has been renamed pike_rusage.h due to old dependencies. Thus I run "make depend". However this fails as well, because make depend compiles Pike. This is no good - make depend should make dependencies! I have to manually edit the 'dependencies' files.
How about using the method used by PExts instead - the configure process creates the dependencies. Works really well I think (does of course make configuration slower).