Extend gendef.pl in preparation for meson

Extend gendef.pl in preparation for meson

The main issue with using gendef.pl as-is for meson is that with meson the
filenames are a bit longer, exceeding the max commandline length when calling
dumpbin with all objects. As it's easier to pass in a library anyway, do so.

The .def file location, input and temporary file location need to be tunable
as well.

This also fixes a bug in gendef.pl: The logic when to regenerate was broken
and never avoid regenerating.

Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/20220809071055.rgikv3qn74ypnnbb@awork3.anarazel.de
Discussion: https://postgr.es/m/7dae5979-c6c0-cec5-7a36-76a85aa8053d@enterprisedb.com