The main reason why this is necessary is that gcc 5.x on Xenial doesn't
support ASan on s390x. Bumping the release to Bionic with gcc 7.x allows
us to build libbpf on s390x with ASan without issues.
As this project uses only Makefile, without any configuration step, and due to
a "non-standard" location of the source files, LGTM kept failing to find the
respective Makefile and build the sources. By tricking LGTM's build system
auto detection, that we use automake/configure, it correctly sets the source
dir, thus the compilation, extraction & analysis steps now work in the src/
subdirectory, as expected.