[iOS][GN] Port ios_web_unittests to build with gn

ios/third_party/gcdwebserver/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 config("public_config") {
-  ldflags = [ "-lz" ]
   libs = [
     "CFNetwork.framework",
     "MobileCoreServices.framework",
+    "z",
   ]
+
   include_dirs = [
     "src/GCDWebServer/Core",
     "src/GCDWebServer/Requests",
     "src/GCDWebServer/Responses",
   ]
 }
 
 config("internal_config") {
   visibility = [ ":gcdwebserver" ]
   cflags_objc = [ "-fobjc-arc" ]
@@ skipping 29 matching lines @@
     "src/GCDWebServer/Responses/GCDWebServerErrorResponse.m",
     "src/GCDWebServer/Responses/GCDWebServerFileResponse.h",
     "src/GCDWebServer/Responses/GCDWebServerFileResponse.m",
     "src/GCDWebServer/Responses/GCDWebServerStreamedResponse.h",
     "src/GCDWebServer/Responses/GCDWebServerStreamedResponse.m",
   ]
 
   public_configs = [ ":public_config" ]
   configs += [ ":internal_config" ]
 }