Add libSDL and emsdk to support building linux and web in container

Dockerfile

@@ -5,11 +5,14 @@ RUN apt-get update && \
         binutils-mips-linux-gnu \
         bsdmainutils \
         build-essential \
+        git \
         libaudiofile-dev \
+        libsdl2-dev \
         pkg-config \
         python3 \
         wget \
-        zlib1g-dev
+        zlib1g-dev && \
+    rm -rf /var/lib/apt/lists/*
 
 RUN wget \
         https://github.com/n64decomp/qemu-irix/releases/download/v2.11-deb/qemu-irix-2.11.0-2169-g32ab296eef_amd64.deb \
@@ -18,9 +21,16 @@ RUN wget \
     dpkg -i qemu.deb && \
     rm qemu.deb
 
+RUN cd /tmp && \
+    git clone https://github.com/emscripten-core/emsdk.git && \
+    cd emsdk && \
+    ./emsdk install latest && \
+    cd .. && \
+    rm -rf emsdk
+
 RUN mkdir /sm64
 WORKDIR /sm64
-ENV PATH="/sm64/tools:${PATH}"
+ENV PATH="/sm64/tools:/emsdk:${PATH}"
 
 CMD echo 'usage: docker run --rm --mount type=bind,source="$(pwd)",destination=/sm64 sm64 make VERSION=${VERSION:-us} -j4\n' \
          'see https://github.com/n64decomp/sm64/blob/master/README.md for advanced usage'