Build riscv64 docker images

Ubuntu focal is chosen as there are no docker images for bionic.

.github/workflows/main.yml

@@ -21,6 +21,8 @@ jobs:
             DIST: 'bionic'
           - ARCH: 'x86_64'
             DIST: 'bionic'
+          - ARCH: 'riscv64'
+            DIST: 'focal'
 
     name: Build ${{ matrix.DIST }}  (${{ matrix.ARCH }})
     env:

Dockerfile.focal-riscv64

@@ -0,0 +1,58 @@
+FROM riscv64/ubuntu:focal
+
+ENV ARCH=riscv64 DIST=focal
+
+# inherited by build scripts
+ARG VERBOSE=0
+
+COPY /entrypoint-ubuntu.sh /entrypoint.sh
+
+ENTRYPOINT ["/entrypoint.sh"]
+SHELL ["/entrypoint.sh", "bash", "-c"]
+
+COPY ./install-deps-ubuntu.sh /
+RUN bash -x /install-deps-ubuntu.sh
+
+COPY ./install-cmake.sh /
+RUN bash -x /install-cmake.sh
+
+ARG DESKTOP_FILE_UTILS_VERSION=56d220dd679c7c3a8f995a41a27a7d6f3df49dea
+COPY build-desktop-file-utils.sh /
+RUN bash -x /build-desktop-file-utils.sh
+
+ARG AUTOMAKE_VERSION=1.16.5
+COPY build-automake.sh /
+RUN bash -x /build-automake.sh
+
+ARG LIBGPG_ERROR_VERSION=1.45
+COPY build-libgpg-error.sh /
+RUN bash -x /build-libgpg-error.sh
+
+ARG LIBASSUAN_VERSION=2.5.5
+COPY build-libassuan.sh /
+RUN bash -x /build-libassuan.sh
+
+ARG LIBGCRYPT_VERSION=1.10.1
+COPY build-libgcrypt.sh /
+RUN bash -x /build-libgcrypt.sh
+
+ARG LIBKSBA_VERSION=1.6.0
+COPY build-libksba.sh /
+RUN bash -x /build-libksba.sh
+
+ARG NPTH_VERSION=1.6
+COPY build-npth.sh /
+RUN bash -x /build-npth.sh
+
+ARG GNUPG_VERSION=2.3.7
+COPY build-gnupg.sh /
+RUN bash -x /build-gnupg.sh
+
+ARG GPGME_VERSION=1.17.1
+COPY build-gpgme.sh /
+RUN bash -x /build-gpgme.sh
+
+# create unprivileged user for non-build-script use of this image
+# build-in-docker.sh will likely not use this one, as it enforces the caller's uid inside the container
+RUN adduser --system --group build
+USER build