Unfortunately this doesn't make all tests compilable due
to all sort of weird and wonderful bad levels includes
on Windows (G referenced from bf_blenlib) but at least
allows to selectively build tests for now.
Main purpose of this is to bring new gflags library which is more likely
to have a fix for undefined order of static variables initialization and
also to bring new glog where some compilation error are fixed (which are
only visible with more strict checks with clang and c++11 enabled).
