Include prebuilt man pages again

Historically, Sphinx was required when building "standalone" builds,
else they would have no man pages.

This means that commit 0709e4be8b (Use standalone code paths by
default, 2025-10-26) broke man pages for users who build from a
tarball where non-standalone builds would use prebuilt docs.

Add a hack to use prebuilt docs again.

In future, we'll remove prebuilt docs, see #12052.

build_tools/make_tarball.sh

@@ -66,13 +66,15 @@ PREFIX_TMPDIR=$(mktemp -d)
 cd "$PREFIX_TMPDIR"
 echo "$VERSION" > version
 cmake -G "$BUILD_GENERATOR" -DCMAKE_BUILD_TYPE=Debug "$wd"
+mkdir $PWD/user_doc/src
 FISH_SPHINX_BUILD_DATE=$tag_creation_date \
+FISH_SPHINX_HELP_SECTIONS_OUTPUT=$PWD/user_doc/src/help_sections.rs \
     $BUILD_TOOL doc
 
 TAR_APPEND="$TAR --append --file=$path --mtime=now --owner=0 --group=0 \
     --mode=g+w,a+rX --transform s/^/$prefix\//"
 $TAR_APPEND --no-recursion user_doc
-$TAR_APPEND user_doc/html user_doc/man
+$TAR_APPEND user_doc/html user_doc/man user_doc/src/help_sections.rs
 $TAR_APPEND version
 
 cd -