Hm, strange. Somehow looks like this old issue...  though various attempts of mine to reproduce the problem with 5.16 have failed (although it seems the patch hasn't made it into current Makefile.SH).

Anyhow, try deleting the link (pod/perl5160delta.pod) manually before re-running make, or add a -f (force) to the respective rule in the (generated) makefile:

pod/perl5160delta.pod: pod/perldelta.pod
        $(LNS) -f perldelta.pod pod/perl5160delta.pod
               ^^
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