doc: handle 'make htmldocs' warnings as errors
Parameter -W for sphinx-build turns build warnings into errors. This helps
us to avoid bad patches passing Gitlab CI.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/Makefile b/doc/Makefile
index 683e4b5..050d9dd 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -6,7 +6,7 @@
# You can set these variables from the command line.
SPHINXBUILD = sphinx-build
-SPHINXOPTS =
+SPHINXOPTS = -W
SPHINXDIRS = .
_SPHINXDIRS = $(patsubst $(srctree)/doc/%/conf.py,%,$(wildcard $(srctree)/doc/*/conf.py))
SPHINX_CONF = conf.py