tree-wide: avoid uninitialized warning on _cleanup_ variables

With some versions of the compiler, the _cleanup_ attr makes it think
the variable might be freed/closed when uninitialized, even though it
cannot happen. The added cost is small enough to be worth the benefit,
and optimized builds will help reduce it even further.

src/basic/efivars.c

@@ -350,7 +350,7 @@ int cache_efi_options_variable(void) {
          * (NB: For testing purposes, we still check the $SYSTEMD_EFI_OPTIONS env var before accessing this
          * cache, even when in SecureBoot mode.) */
         if (is_efi_secure_boot()) {
-                _cleanup_free_ char *k;
+                _cleanup_free_ char *k = NULL;
 
                 k = efi_variable_path(EFI_VENDOR_SYSTEMD, "SystemdOptions");
                 if (!k)

src/basic/path-lookup.c

@@ -772,7 +772,7 @@ void lookup_paths_log(LookupPaths *p) {
                 log_debug("Ignoring unit files.");
                 p->search_path = strv_free(p->search_path);
         } else {
-                _cleanup_free_ char *t;
+                _cleanup_free_ char *t = NULL;
 
                 t = strv_join(p->search_path, "\n\t");
                 log_debug("Looking for unit files in (higher priority first):\n\t%s", strna(t));

src/basic/terminal-util.c

@@ -52,7 +52,7 @@ static volatile int cached_color_mode = _COLOR_INVALID;
 static volatile int cached_underline_enabled = -1;
 
 int chvt(int vt) {
-        _cleanup_close_ int fd;
+        _cleanup_close_ int fd = -1;
 
         /* Switch to the specified vt number. If the VT is specified <= 0 switch to the VT the kernel log messages go,
          * if that's configured. */
@@ -514,7 +514,7 @@ int terminal_vhangup_fd(int fd) {
 }
 
 int terminal_vhangup(const char *name) {
-        _cleanup_close_ int fd;
+        _cleanup_close_ int fd = -1;
 
         fd = open_terminal(name, O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
         if (fd < 0)

src/basic/time-util.c

@@ -1547,7 +1547,7 @@ int time_change_fd(void) {
                 .it_value.tv_sec = TIME_T_MAX,
         };
 
-        _cleanup_close_ int fd;
+        _cleanup_close_ int fd = -1;
 
         assert_cc(sizeof(time_t) == sizeof(TIME_T_MAX));