Generated ID in HTML files are not stable.  They switch between two
values, one is suffixed with "o".  Example:

- <table·class="docutils·align-default"·id="abi-sys-kernel-fadump-enabledo">
+ <table·class="docutils·align-default"·id="abi-sys-kernel-fadump-enabled">

The same ID is re-used later in another file.  So those ID are global
and rely on the order of the input files.

This is out of https://tests.reproducible-builds.org/debian/dbd/unstable/amd64/linux_7.0.4-1.diffoscope.html#linux-doc--.-_-.-.---_all.deb---data.tar.xz---data.tar---.-usr-share-doc-linux-doc--.--html-admin-guide-abi-obsolete.html

As reproducibility is now mandatory and this package is a compiler of
sorts, it needs to be able to produce the same output every time.

Bastian