Prevent xref crashes with undef behaviours

When a given behaviour module does not exist, rebar3 brutally crashes.
This patch makes it so instead, there is a warning output menitoning the
missing behaviour, and this one is omitted from the unused function
calls check. This means that unused calls will instead be shown for the
module implementing a non-existing behaviour, as if no behaviour were
declared in the first place.

0 files changed, 0 insertions, 0 deletions