Do a few test runs to prebuild system libraries and ports.

.gitignore

@@ -0,0 +1,2 @@
+*.swp
+test-*

Dockerfile

@@ -15,4 +15,13 @@ RUN wget https://github.com/Kitware/CMake/releases/download/v3.30.4/cmake-3.30.4
     bash cmake_install.sh --prefix=cmake --skip-license && \
     rm cmake_install.sh
 
+# Prebuilding system libraries so that we don't have to do it again in each use case.
+RUN mkdir test-bar && \
+    touch test-bar/foo.c && \
+    cd test-bar && \
+    emcc --use-port=zlib -pthread --bind foo.c -o alpha \
+    emcc --use-port=zlib -pthread --bind -O3 foo.c -o bravo \
+    cd ../ && \
+    rm -rf test-bar
+
 ENV PATH="/emsdk:/emsdk/upstream/emscripten:/cmake/bin:${PATH}"