Fix OSX issues

+ Fix compiling under OSX. Original code was going the $unix route by
default where ioctl SIOCGARP nor SIOCGIFHWADDR is available
+ Add new code path $osx for OSX based on $bsd, without skipping the
clock_gettime implementation. Now it is possible to implement a new
get_any_mac for OSX targets
+ Disable dollar-in-identifier warnings when compiling with clang
- Commented out local std::string local in printftime function in favor
of the actual locale parameter which was not being used
Merge pull request #2 from filippsen/compile-osx

Fix OSX issues