Normalize background thread configuration.

Also fix a compilation error #ifndef JEMALLOC_PTHREAD_CREATE_WRAPPER.

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -316,6 +316,11 @@
 /* GNU specific sched_setaffinity support */
 #undef JEMALLOC_HAVE_SCHED_SETAFFINITY
 
+/*
+ * If defined, all the features necessary for background threads are present.
+ */
+#undef JEMALLOC_BACKGROUND_THREAD
+
 /*
  * If defined, jemalloc symbols are not exported (doesn't work when
  * JEMALLOC_PREFIX is not defined).

include/jemalloc/internal/jemalloc_preamble.h.in

@@ -168,12 +168,6 @@ static const bool force_ivsalloc =
     false
 #endif
     ;
-
-#if (defined(JEMALLOC_HAVE_PTHREAD) && defined(JEMALLOC_HAVE_DLSYM)	\
-    && !defined(JEMALLOC_OSSPIN) && !defined(JEMALLOC_OS_UNFAIR_LOCK))
-/* Currently background thread supports pthread only. */
-#define JEMALLOC_BACKGROUND_THREAD
-#endif
 static const bool have_background_thread =
 #ifdef JEMALLOC_BACKGROUND_THREAD
     true