Thanks, I installed that and am marking this bug report as done.

I used the opportunity to sync GNU diff with current Gnulib, causing a 
few minor changes to Gnulib.

I also installed the attached patch, to work around more the places 
where Gnulib drags in some multithreading and/or locale code that GNU 
diff (which is single-threaded and not that picky about locales) doesn't 
need. Not sure if these suggest any Gnulib changes.