compat/regex: fix argument order to calloc(3)

compat/regex: fix argument order to calloc(3)

Windows compiler suddenly started complaining that calloc(3) takes
its arguments in <nmemb, size> order.  Indeed, there are many calls
that has their arguments in a _wrong_ order.

Fix them all.

A sample breakage can be seen at

  https://github.com/git/git/actions/runs/9046793153/job/24857988702#step:4:272

[Backported from f01301aabe1 (compat/regex: fix argument order to
calloc(3), 2024-05-11).]

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>