Silence warnings about using offsetof on near-POD structs.

gyp/common_conditions.gypi

 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
     'SK_SUPPORT_GPU=<(skia_gpu)',
     'SK_SUPPORT_OPENCL=<(skia_opencl)',
     'SK_FORCE_DISTANCEFIELD_FONTS=<(skia_force_distancefield_fonts)',
   ],
   'conditions' : [
@@ skipping 157 matching lines @@
           '-Wall',
           '-Wextra',
           '-Winit-self',
           '-Wpointer-arith',
 
           '-Wno-unused-parameter',
         ],
         'cflags_cc': [
           '-fno-rtti',
           '-Wnon-virtual-dtor',
+          '-Wno-invalid-offsetof',  # GCC <4.6 is old-school strict about what is POD.
         ],
         'conditions': [
           [ 'skia_android_framework==0', {
             'cflags': [
               # This flag is not supported by Android build system.
               '-Wno-c++11-extensions',
             ],
           }],
           [ 'skia_warnings_as_errors', {
             'cflags': [
@@ skipping 495 matching lines @@
         'SK_BUILD_JSON_WRITER',
       ]
     }],
 
   ], # end 'conditions'
   # The Xcode SYMROOT must be at the root. See build/common.gypi in chromium for more details
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }