Disable munmap() if it causes VM map holes.

Add a configure test to determine whether common mmap()/munmap()
patterns cause VM map holes, and only use munmap() to discard unused
chunks if the problem does not exist.

Unify the chunk caching for mmap and dss.

Fix options processing to limit lg_chunk to be large enough that
redzones will always fit.

include/jemalloc/internal/jemalloc_internal.h.in

@@ -102,6 +102,13 @@ static const bool config_prof_libunwind =
     false
 #endif
     ;
+static const bool config_munmap =
+#ifdef JEMALLOC_MUNMAP
+    true
+#else
+    false
+#endif
+    ;
 static const bool config_stats =
 #ifdef JEMALLOC_STATS
     true