Update certificates in some Ubuntu 16 images.
These images use crosstool-ng, which needs to download various things off the internet. The certificate for `www.kernel.org` no longer works with the ca-certificates in Ubuntu 16. This resolves the issue by grabbing from a newer image a certificate bundle from https://curl.se/ca/cacert.pem, which is usually somewhat up to date.
+FROM ubuntu:20.04
+RUN apt-get update && \
+ apt-get install -y --no-install-recommends \
+ curl \
+ ca-certificates
+WORKDIR /tmp
+RUN curl -f https://curl.se/ca/cacert.pem -o cacert.pem
+
FROM ubuntu:16.04
+# The ca-certificates in ubuntu-16 is too old, so update the certificates
+# with something more recent.
+COPY --from=0 /tmp/cacert.pem /tmp/cacert.pem
+ENV CURL_CA_BUNDLE /tmp/cacert.pem
+
COPY scripts/cross-apt-packages.sh /scripts/
RUN sh /scripts/cross-apt-packages.sh
+FROM ubuntu:20.04
+RUN apt-get update && \
+ apt-get install -y --no-install-recommends \
+ curl \
+ ca-certificates
+WORKDIR /tmp
+RUN curl -f https://curl.se/ca/cacert.pem -o cacert.pem
+
FROM ubuntu:16.04
+# The ca-certificates in ubuntu-16 is too old, so update the certificates
+# with something more recent.
+COPY --from=0 /tmp/cacert.pem /tmp/cacert.pem
+ENV CURL_CA_BUNDLE /tmp/cacert.pem
+
COPY scripts/cross-apt-packages.sh /scripts/
RUN sh /scripts/cross-apt-packages.sh
+FROM ubuntu:20.04
+RUN apt-get update && \
+ apt-get install -y --no-install-recommends \
+ curl \
+ ca-certificates
+WORKDIR /tmp
+RUN curl -f https://curl.se/ca/cacert.pem -o cacert.pem
+
FROM ubuntu:16.04
+# The ca-certificates in ubuntu-16 is too old, so update the certificates
+# with something more recent.
+COPY --from=0 /tmp/cacert.pem /tmp/cacert.pem
+ENV CURL_CA_BUNDLE /tmp/cacert.pem
+
COPY scripts/cross-apt-packages.sh /scripts/
RUN sh /scripts/cross-apt-packages.sh
+FROM ubuntu:20.04
+RUN apt-get update && \
+ apt-get install -y --no-install-recommends \
+ curl \
+ ca-certificates
+WORKDIR /tmp
+RUN curl -f https://curl.se/ca/cacert.pem -o cacert.pem
+
FROM ubuntu:16.04
+# The ca-certificates in ubuntu-16 is too old, so update the certificates
+# with something more recent.
+COPY --from=0 /tmp/cacert.pem /tmp/cacert.pem
+ENV CURL_CA_BUNDLE /tmp/cacert.pem
+
COPY scripts/cross-apt-packages.sh /scripts/
RUN sh /scripts/cross-apt-packages.sh