[scout] ABI: Expect to use xcrypt for libcrypt.so.1
scout is based on Ubuntu 12.04, which used glibc libcrypt.so.1, but that could make it break when running against a newer glibc on a host system that does not have libcrypt.so.1 (like a default Arch installation). Set it up to use a backport of libcrypt1 instead.
steamrt/tasks#332
/cc @denittis
CI failure is expected until packaging/libxcrypt!2 lands.