sphinx-build -jauto has nondeterministic html results

[bmwiedemann]

Describe the bug
html rendering with -jauto has nondeterministic results, except when run on a 1-core-VM

To Reproduce
Steps to reproduce the behavior:

osc checkout openSUSE:Factory/kernel-docs && cd $_
osc build --noservice
# extract html/Documentation/output/core-api/refcount-vs-atomic.html
# compare to those from another build

or maybe

git clone --depth 1 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
cd linux-2.6
make htmldocs

Expected behavior
output should be deterministic

Your project
https://github.com/torvalds/linux/blob/master/Documentation/conf.py

Screenshots

-<p>Il kernel è scritto nel linguaggio di programmazione C <a class="reference internal" href="../../../process/programming-language.html#href_anchor" id="a_idN"><span>[c-language]</span></a>.
-Più precisamente, il kernel viene compilato con <code class="docutils literal notranslate"><span class="pre">gcc</span></code> <a class="reference internal" href="../../../process/programming-language.html#href_anchor" id="a_idN"><span>[gcc]</span></a> usando
-l’opzione <code class="docutils literal notranslate"><span class="pre">-std=gnu89</span></code> <a class="reference internal" href="../../../process/programming-language.html#href_anchor" id="a_idN"><span>[gcc-c-dialect-options]</span></a>: il dialetto GNU
+<p>Il kernel è scritto nel linguaggio di programmazione C <a class="reference internal" href="#href_anchor" id="a_idN"><span>[c-language]</span></a>.
+Più precisamente, il kernel viene compilato con <code class="docutils literal notranslate"><span class="pre">gcc</span></code> <a class="reference internal" href="#href_anchor" id="a_idN"><span>[gcc]</span></a> usando
+l’opzione <code class="docutils literal notranslate"><span class="pre">-std=gnu89</span></code> <a class="reference internal" href="#href_anchor" id="a_idN"><span>[gcc-c-dialect-options]</span></a>: il dialetto GNU

Environment info

• OS: openSUSE Tumbleweed
• Python version: 3.7.3
• Sphinx version: 2.2.0
• Sphinx extensions: websupport, devhelp, htmlhelp, jsmath, serializinghtml

Additional context
Got same result when adding -E

This bug was found while working on reproducible builds for openSUSE.