/usr/lib/GNUstep/GDLAdaptors-4.9/PostgreSQL.gdladaptor/stamp.make is in libsope1 2.2.9-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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OLD_GNUSTEP_STAMP_ASTRING = _PostgreSQL72Adaptor-