Multiple independent copies of google/glog present in memcached process

As found when trying to fix MB-43525, we currently link multiple copies of the glog library into the memcached process (every place we link Folly). This is a problem because glog doesn't use a suitable singleton to be able to support this usage; meaning you essentially have to initialise and configure it once for every instance which exists.

For example, we cannot address MB-43525 without having to call google::InitGoogleLogging and configure a custom log sink from every place where glog is linked.

To address this we need to end up with just one copy of glog - either by

1. making glog a shared library instead of static, or
2. linking everything which uses glog into a single static binary.