I do not have this missing symbol problem on my Debian unstable box (x86_64 architecture). It is defined by the shared library "/usr/lib/x86_64-linux-gnu/libglog.so.0.0.0" from the "libgoogle-glog0" package (version 0.3.3-1).Upgrading the package to the 0.3.3 unstable version fixed the startup problem.
Thanks for your feedback! I have just fixed the package by introducing a minimal version for Google Log [1].
[1] http://anonscm.debian.org/viewvc/debian-med/trunk/packages/orthanc/trunk/debian/control?r1=15411&r2=15861