From the 8.1 Xcode Beta:
```
There is no Command Line Tools (OS X 10.11) for Xcode 8 package. Xcode 8 contains
SDKs that are incompatible with earlier toolchains. Developers who want to make
use of the Xcode 8 SDKs from the command line must choose the SDK with `xcode-select`.
Developers on OS X El Capitan who have installed versions of the Command Line Tools
(OS X 10.11) for Xcode 8 Beta should install Command Line Tools (OS X 10.11)
for Xcode 7.3.1.
```

Thanks Apple.