How to disable ARC for a single file in Xcode 5?
You appear to be missing the right-hand column. On my install it looks like this:
Notice the 'Compiler Flags' column to the right of the 'Name' column.
Double-clicking anywhere on the row allows me to type into the flags as long as that column is on screen. Making my window sufficiently thin causes it to be invisible so the first thing I'd try is making your window super-wide, to see whether you can get a flags column.