add systemd service file

cmake/modules/systemdservice.cmake

@@ -0,0 +1,21 @@
+########
+# Find systemd service dir
+
+pkg_check_modules(SYSTEMD "systemd")
+if (SYSTEMD_FOUND AND "${SYSTEMD_SERVICES_INSTALL_DIR}" STREQUAL "")
+	execute_process(COMMAND ${PKG_CONFIG_EXECUTABLE}
+		--variable=systemdsystemunitdir systemd
+		OUTPUT_VARIABLE SYSTEMD_SERVICES_INSTALL_DIR)
+	string(REGEX REPLACE "[ \t\n]+" "" SYSTEMD_SERVICES_INSTALL_DIR
+		"${SYSTEMD_SERVICES_INSTALL_DIR}")
+elseif (NOT SYSTEMD_FOUND AND SYSTEMD_SERVICES_INSTALL_DIR)
+	message (FATAL_ERROR "Variable SYSTEMD_SERVICES_INSTALL_DIR is\
+		defined, but we can't find systemd using pkg-config")
+endif()
+
+if (SYSTEMD_FOUND)
+	set(WITH_SYSTEMD "ON")
+	message(STATUS "systemd services install dir: ${SYSTEMD_SERVICES_INSTALL_DIR}")
+else()
+	set(WITH_SYSTEMD "OFF")
+endif (SYSTEMD_FOUND)