BUILD: init: avoid a build warning on FreeBSD with USE_PROCCTL

It was brought by a variable declared after some statements in commit
21185970c ("MINOR: proc: setting the process to produce a core dump on
FreeBSD."). It's worth noting that some versions of clang seem to ignore
-Wdeclaration-after-statement by default. No backport is needed.

src/haproxy.c

@@ -3384,10 +3384,12 @@ int main(int argc, char **argv)
 			ha_warning("[%s.main()] Failed to set the dumpable flag, "
 				   "no core will be dumped.\n", argv[0]);
 #elif defined(USE_PROCCTL)
+		{
 			int traceable = PROC_TRACE_CTL_ENABLE;
 			if (procctl(P_PID, getpid(), PROC_TRACE_CTL, &traceable) == -1)
 				ha_warning("[%s.main()] Failed to set the traceable flag, "
 					   "no core will be dumped.\n", argv[0]);
+		}
 #endif
 	}