lib-link.m4 serial 33
Gnulib upstream has released lib-link.m4 serial 33. We should update our copy.
All branches have serial 32 previously, so updating to 33 is not about to bring in changes other than 32 -> 33 one, which is a bugfix. So I see no reason not to target to S3_0.
Gnulib upstream has released lib-link.m4 serial 33. We should update our copy.