audit: fix external header definitions for gcc10

Header definitions need to be external when building with -fno-common (which is default in GCC 10).

(.text+0x0): multiple definition of `event_node_list'; ausearch.o (symbol
from plugin):(.text+0x0): first defined here [ 60s]
/usr/lib64/gcc/x86_64-suse-linux/9/../../../../x86_64-suse-linux/bin/ld:
ausearch-time.o (symbol from plugin): in function `lookup_time':

Fixes ff25054df7ed

---
 src/ausearch-common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

src/ausearch-common.h +1 -2

index 6669203..3040547 100644
@@ -50,7 +50,7 @@ extern pid_t event_pid;
 extern int event_exact_match;
 extern uid_t event_uid, event_euid, event_loginuid;
 extern const char *event_tuid, *event_teuid, *event_tauid;
-slist *event_node_list;
+extern slist *event_node_list;
 extern const char *event_comm;
 extern const char *event_filename;
 extern const char *event_hostname;
--

2.21.0