Fixes OS X build flags.
Fixes OS X build flags.

tessel/node-usb,marcopiraccini/electron-usb,nonolith/node-usb,SimplyComplexCo/node-usb,marcopiraccini/electron-usb,SimplyComplexCo/node-usb,stberger3040/node-usb,rhuehn/node-usb,stberger3040/node-usb,rhuehn/node-usb,nonolith/node-usb,rhuehn/node-usb,SimplyComplexCo/node-usb,rhuehn/node-usb,SimplyComplexCo/node-usb,nonolith/node-usb,marcopiraccini/electron-usb,tessel/node-usb,marcopiraccini/electron-usb,nonolith/node-usb,stberger3040/node-usb,tessel/node-usb,stberger3040/node-usb,tessel/node-usb,stberger3040/node-usb