Folder was empty. Installed Xcode again and then install was fine. Thanks!
The command line tools are actually installed here:
/Library/Developer/CommandLineTools
I always install using the separate command line tools installer from Apple's dev site (eg, Command_Line_Tools_macOS_10.11_for_Xcode_8.2.dmg).
Xcode.app contains it own copies of the command line tools, but I don't think FPC can use these, Hence, the "xcode-select install" in Getting Started.rtf.