Tweak GYP to also link with XCode 7.

gyp/zlib.gyp

 # Copyright 2014 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'targets': [
   {
     # Only used by win, down below.
     'target_name' : 'zlib_x86_simd',
@@ skipping 12 matching lines @@
           },
         }],
       ],
   },
   {
       'target_name': 'zlib',
       'direct_dependent_settings': {
         'conditions': [
           [ 'skia_android_framework', { 'include_dirs': [ 'external/zlib' ] }],
           [ 'skia_os == "mac" or skia_os == "ios"', {
-              # XCode needs and explicit file path, not a logical name like -lz.
-              'link_settings': { 'libraries': [ '$(SDKROOT)/usr/lib/libz.dylib' ] },
+              # XCode needs a full library name, not -lz.
+              'link_settings': { 'libraries': [ 'libz.dylib' ] },
           }],
           [ 'skia_os not in ["mac", "ios", "win"]',{
               'link_settings': { 'libraries': [ '-lz' ] },
           }]
         ],
       },
       'conditions': [
         [ 'skia_os != "win"', {
           'type': 'none',
         }, {
@@ skipping 41 matching lines @@
           'dependencies': [
             'zlib_x86_simd',
           ],
           'defines': [
             '_CRT_NONSTDC_NO_DEPRECATE',
           ],
         }],
       ],
   }],
 }