Cherry-pick Daniel Gustafsson commit to fix tablefunc extension build

[reshke]

The orig commit message follows:

The tablefunc contrib module lacked the upstream Makefile and test- data. Re-add the upstream files and also add an variable output rule to the regress init_file to make it build and test green.

The extra REGRESS_OPTS flag added to the Makefile can be removed once we can add a single init_file handling for all PGXS modules, but the pipeline is currently not supporting that.

Reviewed-by: Hubert Zhang

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