zeitgeist rc buggy, apparently unmaintained and required by gnome

[peter green]

While looking at why gnome-core is not installable on arm64 official I 
discovered that zeitgeist had failed to build. Further investigation 
found that the same issue had been encountered during an amd64 rebuild 
test and had been reported as 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=763219

Some googling shows this is an issue that other projects using valadoc 
have run into but doesn't provide enough information for someone like me 
who is clueless about valadoc to fix it.

Since the bug report has received no maintainer response yet, there has 
been no maintainer uploads of the package for nearly a year and the 
package seems to be related to gnome* I thought it was reasonable to 
bring this to the gnome teams attention.

P.S. ubuntu disabled the documentation build for unrelated reasons, 
namely that they don't have valadoc in main.

* gnome-core depends on empathy which build-depends on libfolks-dev 
which is built from source package folks which build-depends on 
libzeitgeist-2.0-dev 
<https://buildd.debian.org/status/package.php?p=zeitgeist&suite=sid> 
which is built from source package zeitgeist. Also the vala lanauge 
apppears to be maintained by the gnome project.