INSTALLATION_DIRS, as well as all occurrences of ${PREFIX}/man with
${PREFIX}/${PKGMANDIR}.
Fixes PR 35265, although I did not use the patch provided therein.
xapply (Extended Apply) is an clever derivative of xargs and apply.
Using list or tabular input from one or more descriptors, xapply executes
a template command modified for each input. It supports simple split
on token expression, and has support (a la make -j) for running many
jobs in parallel.
