Use cmake source directory instead of current source dir as working dir. (#250)
Use cmake source directory instead of current source dir as working dir. (#250)

Fixes #249.

* Use CMake source directory instead of current source directory as the working directory in git submodule update for `google-benchmark`, in order to support git versions prior to 1.8.4.
halfflat/arbor,halfflat/arbor,halfflat/arbor,halfflat/nestmc-proto,halfflat/nestmc-proto,halfflat/arbor,eth-cscs/nestmc-proto,halfflat/arbor,eth-cscs/nestmc-proto,eth-cscs/nestmc-proto,halfflat/nestmc-proto