Noticed that the documentation build can stuck on a machine with
many cores (160) and I identified a real sphinx problem:
https://github.com/sphinx-doc/sphinx/issues/10969
Note the parallel can help just for some manuals and it is not critical
for us.
ChangeLog:
* doc/Makefile: Disable -j auto.
#
# You can set these variables from the command line.
-SPHINXOPTS ?= -j auto -q
+
+# Disable parallel reading as it can be very slow on a machine with CPUs:
+# https://github.com/sphinx-doc/sphinx/issues/10969
+
+SPHINXOPTS ?= -q
SPHINXBUILD ?= sphinx-build
PAPER ?=
SOURCEDIR = .