Make min version for OSX be 10.6
Config.x86_darwin
has -macosx-version-min=10.5
. This doesn't build for me on OSX 10.11 with Xcode 6.4. But it does work with 10.6.
Consider changing the min version to 10.6. I don't have any way of testing this on anything older than 10.8 anyway.