Fix the Mac toolchain definition in the GN build.

build/toolchain/gcc_toolchain.gni

 # Copyright (c) 2013 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.
 
 # This template defines a GCC toolchain.
 #
 # It requires the following variables specifying the executables to run:
 #  - cc
 #  - cxx
 #  - ar
 #  - ld
 # and the following which is used in the toolchain_args
 #  - toolchain_cpu_arch  (What "cpu_arch" should be set to when invoking a
 #                         build using this toolchain.)
 #  - toolchain_os  (What "os" should be set to when invoking a build using this
 #                   toolchain.)
 template("gcc_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.cc), "gcc_toolchain() must specify a \"cc\" value")
     assert(defined(invoker.cxx), "gcc_toolchain() must specify a \"cxx\" value")
     assert(defined(invoker.ar), "gcc_toolchain() must specify a \"ar\" value")
-    assert(defined(invoker.ar), "gcc_toolchain() must specify a \"ld\" value")
+    assert(defined(invoker.ld), "gcc_toolchain() must specify a \"ld\" value")
     assert(defined(invoker.toolchain_cpu_arch),
-                   "gcc_toolchain() must specify a \"toolchain_cpu_arch\"")
+           "gcc_toolchain() must specify a \"toolchain_cpu_arch\"")
     assert(defined(invoker.toolchain_os),
-                   "gcc_toolchain() must specify a \"toolchain_os\"")
+           "gcc_toolchain() must specify a \"toolchain_os\"")
 
     # We can't do string interpolation ($ in strings) on things with dots in
     # them. To allow us to use $cc below, for example, we create copies of
     # these values in our scope.
     cc = invoker.cc
     cxx = invoker.cxx
     ar = invoker.ar
     ld = invoker.ld
 
     # Make these apply to all tools below.
@@ skipping 39 matching lines @@
     }
 
     # When invoking this toolchain not as the default one, these args will be
     # passed to the build. They are ignored when this is the default toolchain.
     toolchain_args() {
       cpu_arch = invoker.toolchain_cpu_arch
       os = invoker.toolchain_os
     }
   }
 }