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 (file)
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -6,7 +6,7 @@ subdir-y :=
 
 # 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