Make the Mac build work.

tools/gn/secondary/build/config/compiler/BUILD.gn

 # 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.
 
 # Base compiler configuration.
 config("compiler") {
   includes = [ "//" ]
   if (is_win) {
     cflags = [
       # TODO(brettw) these probably need to be refactored.
       "/Od", "/WX", "/Zi", "/Gy", "/GS", "/RTC1", "/EHsc",
     ]
   } else {
     cflags = [
       # TODO(brettw) obviously this needs to be parameterized.
       "-arch i386",
 
       # See http://crbug.com/32204
       "-fno-strict-aliasing",
 
       "-fno-threadsafe-statics",
       "-fstack-protector-all",
-      "-fvisibility-hidden",
+      "-fvisibility=hidden",
       "-fvisibility-inlines-hidden",
     ]
     # !!! Please keep additions sorted alphabetically.
 
     # TODO(brettw) these should be clang-only.
     # if (is_clang) {
       cflags += [
         "-fcolor-diagnostics",
       ]
     #}
 
     cflags_c = [
       "-std=c99",
     ]
 
     cflags_cc = [
       "-fno-exceptions",
       "-std=gnu++11",
     ]
   }
 
   if (is_mac) {
-    cflags += [
+    # These are used for both compiler and linker flags on Mac.
+    common_mac_flags = [
+      # TODO(brettw) obviously this needs to be parameterized.
+      "-arch i386",
+
       # Set which SDK to use.
       # TODO(brettw) this needs to be configurable somehow.
       "-isysroot", "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk",
 
       "-mmacosx-version-min=10.6",
     ]
+
+    # Mac compiler flags.
+    cflags += [
+      # Without this, the constructors and destructors of a C++ object inside
+      # an Objective C struct won't be called, which is very bad.
+      "-fobjc-call-cxx-cdtors",
+    ]
+    cflags += common_mac_flags
+
+    # Mac linker flags.
+    ldflags = [
+      "-L.",
+
+      # TODO(brettW) I don't understand these options.
+      "-Wl,-rpath,@loader_path/.",
+      "-Wl,-rpath,@loader_path/../../..",
+    ]
+    ldflags += common_mac_flags
   }
 }
 
 # runtime_library -------------------------------------------------------------
 #
 # Sets the runtime library and associated options.
 #
 # We don't bother making multiple versions that are toggle-able since there
 # is more than one axis of control (which makes it complicated) and there's
 # no practical reason for anybody to change this since the CRT must agree.
@@ skipping 44 matching lines @@
 # Toggles between higher and lower warnings for code that is (or isn't)
 # part of Chromium.
 
 config("chromium_code") {
   if (is_win) {
     cflags = [
       "/W4",  # Warning level 4.
     ]
   } else if (is_mac) {
     cflags = [
+      "-Wall",
       "-Werror",
       "-Wextra",
     ]
   }
 }
 config("no_chromium_code") {
   if (is_win) {
     cflags = [
       "/W3",  # Warning level 3.
       "/wd4800",  # Disable warning when forcing value to bool.
@@ skipping 106 matching lines @@
 
         # Clang spots more unused functions.
         "-Wno-unused-function",
 
         # Warns when a const char[] is converted to bool.
         "-Wstring-conversion",
       ]
     #}  #is_clang
   }
 }