Add cosmopolitan test image for Naev.

In theory this could be used to build Naev as an APE binary, using:
https://github.com/jart/cosmopolitan

naev-cosmopolitan/Dockerfile

@@ -0,0 +1,37 @@
+# Build toolchain in build container to save space.
+FROM registry.fedoraproject.org/fedora-minimal:latest AS build 
+
+# Get cosmopolitan release
+WORKDIR /tmp
+RUN microdnf install -y git unzip
+RUN curl -LO https://github.com/jart/cosmopolitan/releases/download/3.3.6/cosmocc-3.3.6.zip && \
+    mkdir -p /usr/local/src/cosmocc-3.3.6 && \
+    unzip cosmocc-3.3.6.zip -d /usr/local/src/cosmocc-3.3.6 
+
+# TODO: Attempt building Naev libraries with cosmo toolchain.
+
+# Build final container
+FROM registry.fedoraproject.org/fedora-minimal:latest
+
+WORKDIR /
+COPY --from=build /usr/local/src/cosmocc-3.3.6 /usr/lib/cosmocc
+
+LABEL org.opencontainers.image.authors "Naev Dev Team"
+LABEL org.opencontainers.image.source "https://github.com/naev/naev-infrastructure"
+LABEL org.opencontainers.image.description "Used to build using cosmopolitan libc project."
+
+# Install dependencies for toolchain
+RUN microdnf install -y gzip zip unzip
+
+# Allows for determining what container scripts are run in.
+ENV IMAGE_NAME "naev-cosmopolitan"
+
+# Add CosmoCC to path
+ENV PATH "$PATH:/usr/lib/cosmocc/bin"
+
+# Force appimages to extract to get around a lack of FUSE in docker. (without some ####ery at least.)
+ENV APPIMAGE_EXTRACT_AND_RUN 1
+
+# Install build tools.
+RUN mkdir -p /tmp/naevBuild
+WORKDIR /tmp/naevBuild