Minijail: add logging for seccomp filter failures.

BUG=chromium-os:33361
TEST=unit tests
TEST=security_Minijail0, security_Minijail_seccomp, platform_CrosDisksArchive

Change-Id: I16cdb8fbcf1cb13f2dee5521f97fb8d0bdbdf93b
Reviewed-on: https://gerrit.chromium.org/gerrit/29053
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Commit-Ready: Jorge Lucangeli Obes <jorgelo@chromium.org>
diff --git a/util.h b/util.h
index 8f0fa7b..09a67dc 100644
--- a/util.h
+++ b/util.h
@@ -26,6 +26,9 @@
 #define info(_msg, ...) \
         syslog(LOG_INFO, "libminijail: " _msg, ## __VA_ARGS__)
 
+extern const char *log_syscalls[];
+extern const size_t log_syscalls_len;
+
 int lookup_syscall(const char *name);
 const char *lookup_syscall_name(int nr);
 char *strip(char *s);