The gflags library was not fully configured to be built as a static
library, only one of two files was changed.
Differential Revision: https://developer.blender.org/D6611
With better directory layout and more proper include
statements we can avoid several local modifications,
such as changing config.h for Windows Glog and the
ones related on pass-through statements in logging
headers in Glog.
This commit also makes unused functions not-a-warning
for external code.
