Enable zlib SIMD optimisations on Mac OS X builds

third_party/zlib/simd_stub.c

 /* simd_stub.c -- stub implementations
 * Copyright (C) 2014 Intel Corporation
 * For conditions of distribution and use, see copyright notice in zlib.h
 */
 #include <assert.h>
 
 #include "deflate.h"
 #include "x86.h"
 
-int x86_cpu_enable_simd;
+int x86_cpu_enable_simd = 0;
 
 void ZLIB_INTERNAL crc_fold_init(deflate_state *const s) {
     assert(0);
 }
 
 void ZLIB_INTERNAL crc_fold_copy(deflate_state *const s,
                                  unsigned char *dst,
                                  const unsigned char *src,
                                  long len) {
     assert(0);
 }
 
 unsigned ZLIB_INTERNAL crc_fold_512to32(deflate_state *const s) {
     assert(0);
     return 0;
 }
 
 void ZLIB_INTERNAL fill_window_sse(deflate_state *s)
 {
     assert(0);
 }
 
 void x86_check_features(void)
 {
 }