configure: redirect sphinx-build check to config.log

Otherwise it's hard to debug whats going on.

Signed-off-by: Alex Bennée <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <[email protected]>

Author: stsquad

configure

@@ -4942,7 +4942,9 @@ has_sphinx_build() {
     # sphinx-build doesn't exist at all or if it is too old.
     mkdir -p "$TMPDIR1/sphinx"
     touch "$TMPDIR1/sphinx/index.rst"
-    "$sphinx_build" $sphinx_werror -c "$source_path/docs" -b html "$TMPDIR1/sphinx" "$TMPDIR1/sphinx/out" >/dev/null 2>&1
+    "$sphinx_build" $sphinx_werror -c "$source_path/docs" \
+                    -b html "$TMPDIR1/sphinx" \
+                    "$TMPDIR1/sphinx/out"  >> config.log 2>&1
 }
 
 # Check if tools are available to build documentation.