die on create-diff-object when all objects have processed

When working on large patches that are bound to have lots of
errors, it can be frustrating to have to re-run the build and wait
after every error you fix. With this patch, you get a chance to see
most (if not all) of the errors you'll be facing, at least across
the different object files.
Since most people don't know what create-diff-object is, maybe something a little more generic like: "$ERROR error(s) encountered"?