fix build for non linux/BSD platforms.

src/background_thread.c

@@ -113,9 +113,7 @@ background_thread_info_init(tsdn_t *tsdn, background_thread_info_t *info) {
 
 static inline bool
 set_current_thread_affinity(int cpu) {
-#ifdef __OpenBSD__
-	return false;
-#else
+#if defined(JEMALLOC_HAVE_SCHED_SETAFFINITY) || defined(JEMALLOC_HAVE_PTHREAD_SETAFFINITY_NP)
 #if defined(JEMALLOC_HAVE_SCHED_SETAFFINITY)
 	cpu_set_t cpuset;
 #else
@@ -146,6 +144,8 @@ set_current_thread_affinity(int cpu) {
 #  endif
 	return ret != 0;
 #endif
+#else
+        return false;
 #endif
 }