When checking if we have the development files for libsystemd's journal
APIs, check for either 'libsystemd >= 209' and 'libsystemd-journal'. If
we find 'libsystemd', define the 'journald' tag, which defaults to using
the 'libsystemd.pc' file. If we find the older 'libsystemd-journal',
define both the 'journald' and 'journald_compat' tags, which causes the
'libsystemd-journal.pc' file to be consulted instead.
Signed-off-by: Nalin Dahyabhai <nalin@redhat.com> (github: nalind)
