Not sure about the bash x test, but the change makes the script succeed. Complains about "too many arguments in line 79" though.
Thanks for reporting, I have fixed this, just download the new sources tarball from the Download page.
Note, however, that the script autogen.sh should only be used for development, for normal use using configure && make && make install should be fine.
Also, the x test is a standard way to check for empty variables and the way you changed it is wrong. Look at the new autogen.sh file to see how to do it properly.