ubuntu: Install buildtools on Ubuntu 16.04

The new requirement for gcc 6.0 or later isn't met by Ubuntu 16.04.

The distro-entry script is also modified to enable buildtools whenever
they have been installed.

Signed-off-by: Paul Barker <[email protected]>

dockerfiles/ubuntu/ubuntu-16.04/ubuntu-16.04-base/Dockerfile

@@ -52,6 +52,13 @@ RUN apt-get update && \
     echo 'dash dash/sh boolean false' | debconf-set-selections && \
     DEBIAN_FRONTEND=noninteractive dpkg-reconfigure dash
 
+# The versions of gcc, tar and other tools found in Ubuntu 16.04 are now too
+# old to build recent Yocto Project releases. Install the buildtools tarball to
+# provide the required tools.
+COPY install-buildtools.sh /
+RUN bash /install-buildtools.sh && \
+    rm /install-buildtools.sh
+
 COPY build-install-dumb-init.sh /
 RUN  bash /build-install-dumb-init.sh && \
      rm /build-install-dumb-init.sh && \