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.
Seems we can not use include directories order trick, since
files are included form inside ".." string, which forces current
directory to be checked first.
I've been using this fix in another branch locally, so it seems to work fine.
The other #ifdef checks should be checked on too, as __MINGW32__ and __MINGW64__
do NOT seem to be defined when compiling that file
