BUG/MINOR: haproxy: fix compilation on macOS

Fix the warning treated as error on the CI for the macOS compilation :
"src/haproxy.c:2939:23: error: unused variable 'set'
 [-Werror,-Wunused-variable]"

This does not need to be backported.
diff --git a/src/haproxy.c b/src/haproxy.c
index b89c517..e19b814 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2936,10 +2936,11 @@
 		    proc < MAX_PROCS &&       /* only the first 32/64 processes may be pinned */
 		    ha_cpuset_count(&global.cpu_map.proc[proc])) {   /* only do this if the process has a CPU map */
 
-			struct hap_cpuset *set = &global.cpu_map.proc[proc];
 #ifdef __FreeBSD__
+			struct hap_cpuset *set = &global.cpu_map.proc[proc];
 			ret = cpuset_setaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID, -1, sizeof(set->cpuset), &set->cpuset);
 #elif defined(__linux__) || defined(__DragonFly__)
+			struct hap_cpuset *set = &global.cpu_map.proc[proc];
 			sched_setaffinity(0, sizeof(set->cpuset), &set->cpuset);
 #endif
 		}