osx build config improvments
osx build config improvments

 - no need to support 10.7 so explicitly only support 10.8 (for c++11)
 - use `-Wl,-bind_at_load` to catch undefined symbols at link time rather than runtime
 - use official gyp way of asking for c++11

KnockSoftware/node-osrm,oxidase/node-osrm,oxidase/node-osrm,KnockSoftware/node-osrm,oxidase/node-osrm,Project-OSRM/node-osrm,Project-OSRM/node-osrm,KnockSoftware/node-osrm,KnockSoftware/node-osrm,Project-OSRM/node-osrm