Builds of mupdf for different OS/archs.

Based on:

commit 8f0b2196a8237a5e64ebbe43119be3f30636173c (golden/master)
Author: Robin Watts <Robin.Watts@artifex.com>
Date:   Tue May 18 12:24:55 2021 +0100

    Update ensure_initial_incremental_contents to take the expected length.

    This will allow us to cope with doing 'incremental' writes to/from
    files that have extra information at the end that should be dropped.
    This will be useful when we come to write incrementally from files
    that have been 'snapshotted' and we want to write again while
    dropping the last (transient) xref on those files.