With GCC, at least, you can guarantee that it's thread-safe. (Of course, in some pathological cases you can get then get deadlocks during global static initialisation. C++ is such a lovely language!)
Also, I don't think Google's style guide is the be-all-and-end-all of good C++ style. Virtually non of Boost's code would comply with it. "We do not use C++ exceptions" indeed!