Building with systemd support should not depend on systemd itself.

Why do we care if systemd is installed? We shouldn't.

Trying to build 0.2.6.8 with --enable-systemd blows up with:

checking for SYSTEMD... yes
checking for SYSTEMD209... no
configure: error: Package requirements (systemd >= 209) were not met:

No package 'systemd' found

cf. https://buildd.debian.org/status/fetch.php?pkg=tor&arch=s390x&ver=0.2.6.8-1&stamp=1432377274

--- a/configure.ac
+++ b/configure.ac
@@ -131,7 +131,7 @@ if test x$have_systemd = xyes; then
     AC_DEFINE(HAVE_SYSTEMD,1,[Have systemd])
     TOR_SYSTEMD_CFLAGS="${SYSTEMD_CFLAGS}"
     TOR_SYSTEMD_LIBS="${SYSTEMD_LIBS}"
-    PKG_CHECK_MODULES(SYSTEMD209, [systemd >= 209],
+    PKG_CHECK_MODULES(LIBSYSTEMD209, [libsystemd >= 209],
          [AC_DEFINE(HAVE_SYSTEMD_209,1,[Have systemd v209 or more])], [])
 fi
 AC_SUBST(TOR_SYSTEMD_CFLAGS)