Update leveldb-subtree subtree to latest upstream

Author: fanquake

src/leveldb/util/env_posix.cc

@@ -49,7 +49,7 @@ constexpr const int kDefaultMmapLimit = (sizeof(void*) >= 8) ? 4096 : 0;
 int g_mmap_limit = kDefaultMmapLimit;
 
 // Common flags defined for all posix open operations
-#if defined(HAVE_O_CLOEXEC)
+#if HAVE_O_CLOEXEC
 constexpr const int kOpenBaseFlags = O_CLOEXEC;
 #else
 constexpr const int kOpenBaseFlags = 0;