pbulk-index-item prints a number of variables used by the parallel bulk
build code during either the build, the report or the upload phase.
pbulk-index checks whether multiple versions of the current package
could be build (e.g. because multiple Python versions are supported) and
uses pbulk-index-item for each possible combination.
Thanks to David Laight for explaining the different between using :[#]
in the body of a make target and in a clause of an .if.
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