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 1034 matching lines @@
     'directx_sdk_default_path': '<(DEPTH)/third_party/directxsdk/files',
 
     # Whether we are using the rlz library or not.  Platforms like Android send
     # rlz codes for searches but do not use the library.
     'enable_rlz%': 0,
 
     # MDNS is disabled by default.
     'enable_mdns%' : 0,
 
     'conditions': [
+      # 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.
+      # TODO(glider): set clang to 1 earlier for ASan and TSan builds so that
+      # it takes effect here.
+      ['os_posix==1 and OS!="mac" and OS!="ios" and clang==0 and asan==0 and tsan==0 and msan==0', {
+        'gcc_version%': '<!(python <(DEPTH)/build/compiler_version.py)',
+      }, {
+        'gcc_version%': 0,
+      }],
       ['OS=="win" and "<!(python <(DEPTH)/build/dir_exists.py <(windows_sdk_default_path))"=="True"', {
         'windows_sdk_path%': '<(windows_sdk_default_path)',
       }, {
         'windows_sdk_path%': 'C:/Program Files (x86)/Windows Kits/8.0',
       }],
       ['OS=="win" and "<!(python <(DEPTH)/build/dir_exists.py <(directx_sdk_default_path))"=="True"', {
         'directx_sdk_path%': '<(directx_sdk_default_path)',
       }, {
         'directx_sdk_path%': '$(DXSDK_DIR)',
       }],
       ['OS=="win"', {
         'windows_driver_kit_path%': '$(WDK_DIR)',
         # Set the python arch to prevent conflicts with pyauto on Win64 build.
         # TODO(jschuh): crbug.com/177664 Investigate Win64 pyauto build.
         'python_arch%': 'ia32',
       }],
       # If use_official_google_api_keys is already set (to 0 or 1), we
       # do none of the implicit checking.  If it is set to 1 and the
       # internal keys file is missing, the build will fail at compile
       # time.  If it is set to 0 and keys are not provided by other
       # means, a warning will be printed at compile time.
       ['use_official_google_api_keys==2', {
         'use_official_google_api_keys%':
             '<!(python <(DEPTH)/google_apis/build/check_internal.py <(DEPTH)/google_apis/internal/google_chrome_api_keys.h)',
       }],
       ['os_posix==1 and OS!="mac" and OS!="ios"', {
         # Figure out the python architecture to decide if we build pyauto.
         'python_arch%': '<!(<(DEPTH)/build/linux/python_arch.sh <(sysroot)/usr/<(system_libdir)/libpython<(python_ver).so.1.0)',
         'conditions': [
-          # TODO(glider): set clang to 1 earlier for ASan and TSan builds so
-          # that it takes effect here.
-          ['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,
-          }],
           ['target_arch=="mipsel"', {
             'werror%': '',
             'disable_nacl%': 1,
             'nacl_untrusted_build%': 0,
             'linux_use_tcmalloc%': 0,
             'linux_breakpad%': 0,
             'sysroot%': '<(sysroot)',
             'CXX%': '<(CXX)',
           }],
           # All Chrome builds have breakpad symbols, but only process the
@@ skipping 1607 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"
+    # 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',
   },
 }