Move sparc64 Docker image to Ubuntu

ci/docker/sparc64-unknown-linux-gnu/Dockerfile

-FROM debian:stretch
+FROM ubuntu:18.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         curl ca-certificates \
         gcc libc6-dev \
         gcc-sparc64-linux-gnu libc6-dev-sparc64-cross \
         qemu-system-sparc64 openbios-sparc seabios ipxe-qemu \
-        p7zip-full cpio linux-libc-dev-sparc64-cross linux-headers-4.9.0-3-common
-
-# Put linux/module.h into the right spot as it is not shipped by debian
-RUN cp /usr/src/linux-headers-4.9.0-3-common/include/uapi/linux/module.h /usr/sparc64-linux-gnu/include/linux/
+        p7zip-full cpio linux-libc-dev-sparc64-cross
 
 COPY linux-sparc64.sh /
 RUN bash /linux-sparc64.sh