fix spew in open source build

These constants are defined in ##folly/Malloc.h## which is being pulled in before the jemalloc and spewing in open source builds.

Closes #673

hphp/runtime/vm/class.h

@@ -19,9 +19,6 @@
 
 #include <bitset>
 #include "tbb/concurrent_hash_map.h"
-#ifdef USE_JEMALLOC
-# include <jemalloc/jemalloc.h>
-#endif
 #include <atomic>
 
 #include "hphp/runtime/vm/core_types.h"

hphp/util/alloc.h

@@ -33,6 +33,8 @@
 #  include "malloc.h"
 # endif
 #else
+# undef ALLOCM_ZERO
+# undef ALLOCM_NO_MOVE
 # include <jemalloc/jemalloc.h>
 # ifndef ALLOCM_ARENA
 #  define ALLOCM_ARENA(a) 0