[Reland] Mojo: Eliminate duplicate C API symbols

mojo/mojo_edk_nacl.gyp

 # 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.
 
 {
+  'variables': {
+    'chromium_code': 1,
+  },
   'includes': [
     '../build/common_untrusted.gypi',
-    'mojo_variables.gypi',
   ],
   'target_defaults' : {
    'include_dirs': [
      '..',
    ],
   },
   'targets': [
     {
       # GN version: //mojo/edk/system
       'target_name': 'mojo_system_impl_nacl',
       'type': 'none',
       'variables': {
         'nacl_untrusted_build': 1,
         'nlib_target': 'libmojo_system_impl_nacl.a',
         'build_glibc': 0,
         'build_newlib': 0,
         'build_irt': 1,
         'build_pnacl_newlib': 0,
         'build_nonsfi_helper': 1,
       },
       'dependencies': [
         '../base/base_nacl.gyp:base_nacl',
         '../base/base_nacl.gyp:base_nacl_nonsfi',
         '../base/third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',
-        'mojo_public.gyp:mojo_system_headers',
+        'mojo_public.gyp:mojo_public_system',
       ],
       'defines': [
         'MOJO_SYSTEM_IMPL_IMPLEMENTATION',
-        'MOJO_SYSTEM_IMPLEMENTATION',
-        'MOJO_USE_SYSTEM_IMPL',
       ],
       'sources': [
         'edk/embedder/configuration.h',
         'edk/embedder/embedder.cc',
         'edk/embedder/embedder.h',
         'edk/embedder/embedder_internal.h',
         'edk/embedder/entrypoints.cc',
         'edk/embedder/platform_channel_pair.cc',
         'edk/embedder/platform_channel_pair.h',
         'edk/embedder/platform_channel_pair_posix.cc',
@@ skipping 70 matching lines @@
         'edk/system/watcher.h',
         'edk/system/watcher_set.cc',
         'edk/system/watcher_set.h',
         # Test-only code:
         # TODO(vtl): It's a little unfortunate that these end up in the same
         # component as non-test-only code. In the static build, this code
         # should hopefully be dead-stripped.
         'edk/embedder/test_embedder.cc',
         'edk/embedder/test_embedder.h',
       ],
-      'all_dependent_settings': {
-        # Ensures that dependent projects import the core functions on Windows.
-        'defines': ['MOJO_USE_SYSTEM_IMPL'],
-      },
     },
   ],
 }