Allow for systemd socket activation

If spawned via systemd's socket activation mechanism, use that socket
instead of opening a new one to listen on.

Change-Id: Ia35110902b30b08355edf2fe4041e8377582e72c
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9ca29d9..591734b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -154,6 +154,7 @@
 target_link_libraries(bmcweb ${OPENSSL_LIBRARIES})
 target_link_libraries(bmcweb ${ZLIB_LIBRARIES})
 target_link_libraries(bmcweb pam)
+target_link_libraries(bmcweb -lsystemd)
 target_link_libraries(bmcweb -lstdc++fs)
 add_dependencies(bmcweb tinyxml2_static)
 target_link_libraries(bmcweb tinyxml2_static)