Depending on the system used, t/*.pl may not be expanded into a list of
tests which can be consumed by prove when attempting to run TAP tests on
a given path.  Fix that by using glob() directly in the script, to make
sure that a complete list of tests is provided.  This has not proved to
be an issue with MSVC as the list was properly expanded, but it is on
Linux with perl's system().

This is extracted from a larger patch.

Author: Tom Lane
Discussion: https://postgr.es/m/6628.1567958876@sss.pgh.pa.us
Backpatch-through: 9.4