buildsystem: Check for libsystemd not libsystemd-journal
buildsystem: Check for libsystemd not libsystemd-journal

Starting with systemd 200 (released 2014-02-20) libsystemd-journal is
part of libsystemd instead of a seperate helper library. Thus Check for
libsystemd instead.

Signed-off-by: Sjoerd Simons <1371fd10dd05a897e5b55dc6ae4fbafa1f84c6ec@collabora.co.uk>

GNOME/libgsystem,GNOME/libgsystem