Changed OS X SDK from 'OS X 10.7' to 'Latest OS X'

Git converted the line endings, but the salient change is:

```
- SDKROOT = macosx10.7
+ SDKROOT = macosx
```

The OS X 10.7 SDK is not available in the latest versions of Xcode, and the only use of the OS X SDK is `osxfilebridge.mm`.

Without this change and without manually changing every generated Xcode target, every project fails to build in recent versions of Xcode.

See #1 point 2