Followup comments from https://codereview.chromium.org/298893007/

build/standalone.gypi

 # Copyright 2014 PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Definitions to be used when building stand-alone PDFium binaries.
 
 {
   'variables': {
     'component%': 'static_library',
     'clang%': 0,
@@ skipping 19 matching lines @@
               'host_arch%': 'ia32',
             }],
           ],
         },
         'host_arch%': '<(host_arch)',
         'target_arch%': '<(host_arch)',
       },
       'host_arch%': '<(host_arch)',
       'target_arch%': '<(target_arch)',
     },
+    # These two are needed by V8.
     'host_arch%': '<(host_arch)',
     'target_arch%': '<(target_arch)',
     'werror%': '-Werror',
     'v8_optimized_debug%': 0,
     'icu_gyp_path': '../v8/third_party/icu/icu.gyp',
     'conditions': [
       ['OS == "win"', {
         'os_posix%': 0,
       }, {
         'os_posix%': 1,
@@ skipping 77 matching lines @@
               '-ffunction-sections',
               '-O2',
             ],
           }],
         ],  # conditions
       },
     },
     'defines!': [
       'DEBUG',
     ],
-    'cflags!': [
+    'cflags': [
       '-Wall',
       '-W',
       '-Wno-unused-parameter',
       '-pthread', '-fno-exceptions',
       '-fvisibility=hidden',
     ],
     'cflags_cc': [
       '-Wnon-virtual-dtor',
       '-fno-rtti',
     ],
@@ skipping 91 matching lines @@
       'target_defaults': {
         'target_conditions': [
           ['_type!="static_library"', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-search_paths_first']},
           }],
         ],  # target_conditions
       },  # target_defaults
     }],  # OS=="mac"
   ],
 }