build-sys: use -Og instead of -O0 to catch warnings

  $ touch src/core/dbus.c; make CFLAGS=-O0
  make --no-print-directory all-recursive
  Making all in .
    CC       src/core/libsystemd_core_la-dbus.lo
    CCLD     libsystemd-core.la

  $ touch src/core/dbus.c; make CFLAGS=-Og
  make --no-print-directory all-recursive
  Making all in .
    CC       src/core/libsystemd_core_la-dbus.lo
  src/core/dbus.c: In function 'init_registered_system_bus':
  src/core/dbus.c:798:18: warning: 'id' may be used uninitialized in this function [-Wmaybe-uninitialized]
           dbus_free(id);
                    ^
    CCLD     libsystemd-core.la

-Og Optimize debugging experience. -Og enables optimizations that do
not interfere with debugging. It should be the optimization level of
choice for the standard edit-compile-debug cycle, offering a
reasonable level of optimization while maintaining fast compilation
and a good debugging experience.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/core/manager.c b/src/core/manager.c
index 01db2b0be9..60c22e31d7 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -2062,7 +2062,7 @@ void manager_dispatch_bus_query_pid_done(
 
 int manager_open_serialization(Manager *m, FILE **_f) {
         char *path = NULL;
-        int fd;
+        int fd = -1;
         FILE *f;
 
         assert(_f);