Add emscripten stuff to base build image.

Dockerfile-ubuntu2004

-FROM ubuntu:20.04
+FROM ubuntu:20.04 AS build1
 
 MAINTAINER Ray Burgemeestre
 
     rm -rf cmake-3.21.3 && \
     rm -rf cmake-3.21.3.tar.gz
 
+# Install emscripten deps
+RUN sudo apt-get update && \
+    sudo apt-get install -y libsdl2-dev && \
+    (git clone https://github.com/emscripten-core/emsdk.git || true) && \
+    pushd emsdk && \
+    ./emsdk install latest && \
+    ./emsdk activate latest && \
+    sudo cp -prv ./emsdk_env.sh /etc/profile.d/
+
+# Warmup emscripten (this will pre-fetch SDL2, and cache it)
+RUN /emsdk/upstream/emscripten/em++ -s WASM=1 -s USE_SDL=2 -s USE_SDL_TTF=2 -O3 /dev/null || true
+
 # Fix some weird linker issue CAF build runs into. (fails to link -lc++abi)
 RUN cp -prv /usr/lib/llvm-12/lib/libc++abi.so.1.0 /usr/lib/llvm-12/lib/libc++abi.so
 
 
 RUN chmod +x /usr/local/bin/switch-to-latest-clang
 
+FROM scratch
+
+COPY --from=build1 / /
+
 CMD "/bin/bash"

fmt/Makefile

 ubuntu2004:
 	git clone https://github.com/rayburgemeestre/fmt --branch 7.1.3
 	bash ../ubuntu2004.sh make impl
+	bash ../ubuntu2004.sh make impl-emscripten
 	make package-ubuntu2004
 	bash ../ubuntu2004.sh chown $$(id -u):$$(id -g) . -R  # fix permissions
 
 	make -j $$(nproc) && \
 	make install
 
+impl-emscripten:
+	switch-to-latest-clang
+	apt-get update && apt-get install libz-dev -y && \
+	pushd fmt && \
+	mkdir build2 && pushd build2 && \
+	CXX=/emsdk/upstream/emscripten/em++ cmake -DCMAKE_C_FLAGS=-fPIC -DCMAKE_CXX_FLAGS=-fPIC -DCMAKE_INSTALL_PREFIX=$$PWD/fmt_out2 .. && \
+	make -j $$(nproc) && \
+	make install
+
 package-ubuntu2004:
 	rm -rf out
 	mkdir -p out/opt/cppse/build/fmt
 	cp -prv fmt/build/fmt_out/* out/opt/cppse/build/fmt/
+	cp -prv fmt/build/fmt_out2/lib/libfmt.a out/opt/cppse/build/fmt/lib/libfmt-em.a
 	rm -rf fmt_*_amd64.deb
 	docker run -v "$$(pwd):/src/" rayburgemeestre/fpm-ubuntu:20.04 fpm -v 1.1 -s dir -t deb -n fmt --license MPL2 --maintainer "Ray Burgemeestre <ray@cppse.nl>" --description "fmt - build dependency" --url "https://github.com/mattgodbolt/fmt" --deb-generate-changes -C /src/out