Tweak position of $(DLL_DEFFILE) in shared-library link commands.

Reading the GNU ld man page suggests that this is order-sensitive
and should go in front of library references.  Correction to commit
846e91e0223cf9f2821c3ad4dfffffbb929cb027.
doc: Postgres date-style date-only output is ISO

Backpatch to 9.3

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