BUILD/CLEANUP: systemd: avoid a warning due to mixed code and declaration

Gcc complains because the systemd wrapper mixed code and declaration :
"warning: ISO C90 forbids mixed declarations and code
[-Wdeclaration-after-statement]".
diff --git a/src/haproxy-systemd-wrapper.c b/src/haproxy-systemd-wrapper.c
index 8602881..e588af9 100644
--- a/src/haproxy-systemd-wrapper.c
+++ b/src/haproxy-systemd-wrapper.c
@@ -163,6 +163,7 @@
 int main(int argc, char **argv)
 {
 	int status;
+	struct sigaction sa;
 
 	wrapper_argc = argc;
 	wrapper_argv = argv;
@@ -170,7 +171,6 @@
 	--argc; ++argv;
 	init(argc, argv);
 
-	struct sigaction sa;
 	memset(&sa, 0, sizeof(struct sigaction));
 	sa.sa_handler = &signal_handler;
 	sigaction(SIGUSR2, &sa, NULL);