chore(docs) add latexmk to dependencies and cache examples

scripts/build_html_examples.sh

@@ -1,5 +1,6 @@
 #!/bin/bash
 set -e
+export PATH="/usr/lib/ccache:/usr/local/opt/ccache/libexec:$PATH"
 CURRENT_REF="$(git rev-parse HEAD)"
 rm -rf emscripten_builder
 git clone https://github.com/lvgl/lv_sim_emscripten.git emscripten_builder
@@ -12,8 +13,8 @@ cd ..
 git submodule update --init -- lv_drivers
 mkdir cmbuild
 cd cmbuild
-emcmake cmake .. -DLVGL_CHOSEN_DEMO=lv_example_noop
-make -j$(nproc)
+emcmake cmake .. -DLVGL_CHOSEN_DEMO=lv_example_noop -DCMAKE_C_COMPILER_LAUNCHER=ccache -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
+emmake make -j$(nproc)
 rm -rf CMakeFiles
 cd ../..
 cp -a emscripten_builder/cmbuild docs/_static/built_lv_examples