ci: Build API reference separately

We don't want to spend a lot of time on it just to check the build.

.gitlab-ci/test-docker-autotools.sh

@@ -5,19 +5,31 @@ set -e
 mkdir -p _ccache
 export CCACHE_BASEDIR="$(pwd)"
 export CCACHE_DIR="${CCACHE_BASEDIR}/_ccache"
+export N_PROCS=$(($(nproc) - 1))
+
+EXTRA_CONFIGURE_OPT=""
+
+# Only enable documentation when distchecking, since it's required
+if [ -n "${DO_DISTCHECK-}" ]; then
+    EXTRA_CONFIGURE_OPTS="${EXTRA_CONFIGURE_OPTS} --enable-gtk-doc"
+fi
+
+NOCONFIGURE=1 ./autogen.sh
 
 mkdir _build
 cd _build
-../autogen.sh \
+
+../configure \
     --enable-cloudproviders \
     --enable-broadway-backend \
     --enable-wayland-backend \
     --enable-x11-backend \
     --enable-xinerama \
-    --enable-gtk-doc
-make -j8
+    ${EXTRA_CONFIGURE_OPTS}
+
+make -j${N_PROCS}
 
 if [ -n "${DO_DISTCHECK-}" ]; then
-  make -j8 check SKIP_GDKTARGET="echo Not actually running tests for now"
-  make -j8 distcheck SKIP_GDKTARGET="echo Not actually running tests for now"
+  make -j${N_PROCS} check SKIP_GDKTARGET="echo Not actually running tests for now"
+  make -j${N_PROCS} distcheck SKIP_GDKTARGET="echo Not actually running tests for now"
 fi