meson: don't pass libsystemd version to C preprocessor

We don't use it anymore, and on some systems it's apparently
not an integer.

NEWS

@@ -10,6 +10,7 @@ Bugfixes
 --------
 - tls: fix compilation to support net.tls_sticket_secret() (!1021)
 - validator: ignore bogus RRSIGs present in insecure domains (!1022, #587)
+- build if libsystemd version isn't detected as integer (#592, !1029)
 
 
 Knot Resolver 5.1.2 (2020-07-01)

daemon/main.c

@@ -34,7 +34,7 @@
 
 #include <lua.h>
 #include <uv.h>
-#if SYSTEMD_VERSION > 0
+#if ENABLE_LIBSYSTEMD
 #include <systemd/sd-daemon.h>
 #endif
 #include <libknot/error.h>
@@ -277,7 +277,7 @@ static int run_worker(uv_loop_t *loop, struct engine *engine, fd_array_t *ipc_se
 	memcpy(&engine->ipc_set, ipc_set, sizeof(*ipc_set));
 
 	/* Notify supervisor. */
-#if SYSTEMD_VERSION > 0
+#if ENABLE_LIBSYSTEMD
 	sd_notify(0, "READY=1");
 #endif
 	/* Run event loop */

meson.build

@@ -165,8 +165,7 @@ conf_data.set_quoted('libzscanner_SONAME',
   libzscanner.get_pkgconfig_variable('soname'))
 conf_data.set_quoted('libknot_SONAME',
   libknot.get_pkgconfig_variable('soname'))
-conf_data.set('SYSTEMD_VERSION',
-  libsystemd.found() ? libsystemd.version().to_int() : -1)
+conf_data.set('ENABLE_LIBSYSTEMD', libsystemd.found() ? 1 : 0)
 conf_data.set('NOVERBOSELOG', not verbose_log)
 conf_data.set('ENABLE_SENDMMSG', sendmmsg.to_int())
 conf_data.set('ENABLE_CAP_NG', capng.found())