Expand the -C argument via ‘eval’ in bash completion

Previously completion would not work for ‘ninja -C $HOME/Source/foo targ‸’.

We still do not support using tilde in the directory argument.

misc/bash-completion

@@ -31,7 +31,7 @@ _ninja_target() {
 					C) dir="$OPTARG" ;;
 				esac
 			done;
-			targets_command="ninja -C ${dir} -t targets all"
+			targets_command="eval ninja -C \"${dir}\" -t targets all"
 			targets=$((${targets_command} 2>/dev/null) | awk -F: '{print $1}')
 			COMPREPLY=($(compgen -W "$targets" -- "$cur"))
 		fi