Always define the `gcc_version' variable to some value.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 877 matching lines @@
     # sandbox the zygote process and, thus, all renderer processes.
     'linux_sandbox_path%': '',
 
     # Set this to true to enable SELinux support.
     'selinux%': 0,
 
     # Clang stuff.
     'clang%': '<(clang)',
     'make_clang_dir%': 'third_party/llvm-build/Release+Asserts',
 
+    # The version of GCC in use, set later in platforms that use GCC and have
+    # not explicitly chosen to build with clang. Currently, this means all
+    # platforms except Windows, Mac and iOS.
+    'gcc_version%': 0,

[Paweł Hajdan Jr., 2013/04/26 17:02:07]

We already have a block like:

          ['clang==0 and asan==0 and tsan==0 and msan==0', {
            # This will set gcc_version to XY if you are running gcc X.Y.*.
            # This is used to tweak build flags for gcc 4.5.
            'gcc_version%': '<!(python <(DEPTH)/build/compiler_version.py)',
          }, {
            'gcc_version%': 0,
          }],

in this file. Please extract it and update the condition. This will make
gcc_version defined in only one place, making it easier to reason about.

+
     # These two variables can be set in GYP_DEFINES while running
     # |gclient runhooks| to let clang run a plugin in every compilation.
     # Only has an effect if 'clang=1' is in GYP_DEFINES as well.
     # Example:
     #     GYP_DEFINES='clang=1 clang_load=/abs/path/to/libPrintFunctionNames.dylib clang_add_plugin=print-fns' gclient runhooks
 
     'clang_load%': '',
     'clang_add_plugin%': '',
 
     # The default type of gtest.
@@ skipping 1802 matching lines @@
           },
           'profile': {
             'cflags': ['-pg', '-g'],
             'ldflags': ['-pg'],
           },
           'symbols': {
             'cflags': ['-g'],
           },
         },
         'conditions': [
-          # Don't warn about the "typedef 'foo' locally defined but not used"
-          # for gcc 4.8.
-          # TODO: remove this flag once all builds work. See crbug.com/227506
-          [ 'gcc_version>=48', {
-            'cflags': [
-              '-Wno-unused-local-typedefs',
-            ],
-          }],
           ['target_arch=="ia32"', {
             'target_conditions': [
               ['_toolset=="target"', {
                 'asflags': [
                   # Needed so that libs with .s files (e.g. libicudata.a)
                   # are compatible with the general 32-bit-ness.
                   '-32',
                 ],
                 # All floating-point computations on x87 happens in 80-bit
                 # precision.  Because the C and C++ language standards allow
@@ skipping 1442 matching lines @@
         },
       },
     }],
     ['enable_new_npdevice_api==1', {
       'target_defaults': {
         'defines': [
           'ENABLE_NEW_NPDEVICE_API',
         ],
       },
     }],
+    # Don't warn about the "typedef 'foo' locally defined but not used"

[Paweł Hajdan Jr., 2013/04/26 17:02:07]

Why is this code being moved?

+    # for gcc 4.8.
+    # TODO: remove this flag once all builds work. See crbug.com/227506
+    ['gcc_version>=48', {
+      'target_defaults': {
+        'cflags': [
+          '-Wno-unused-local-typedefs',
+        ],
+      },
+    }],
     ['clang==1', {
       'conditions': [
         ['OS=="android"', {
           # Android could use the goma with clang.
           'make_global_settings': [
             ['CC', '<!(/bin/echo -n ${ANDROID_GOMA_WRAPPER} ${CHROME_SRC}/<(make_clang_dir)/bin/clang)'],
             ['CXX', '<!(/bin/echo -n ${ANDROID_GOMA_WRAPPER} ${CHROME_SRC}/<(make_clang_dir)/bin/clang++)'],
             ['LINK', '<!(/bin/echo -n ${ANDROID_GOMA_WRAPPER} ${CHROME_SRC}/<(make_clang_dir)/bin/clang++)'],
             ['CC.host', '$(CC)'],
             ['CXX.host', '$(CXX)'],
@@ skipping 85 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }