Use new systemd pkgconfig file

libsystemd-{journal,login,id128,daemon} were merged into a single
libsystemd with systemd >=209. there were stubs though which were
removed with >=229

cmake/FindJournald.cmake

@@ -15,7 +15,7 @@
 # use pkg-config to get the directories and then use these values
 # in the FIND_PATH() and FIND_LIBRARY() calls
 find_package(PkgConfig)
-pkg_check_modules(PC_JOURNALD QUIET libsystemd-journal)
+pkg_check_modules(PC_JOURNALD QUIET systemd)
 
 set(JOURNALD_FOUND ${PC_JOURNALD_FOUND})
 set(JOURNALD_DEFINITIONS ${PC_JOURNALD_CFLAGS_OTHER})