Use -fno-delete-null-pointer-checks with gcc builds

gypfiles/toolchain.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 1080 matching lines @@
         ],
       }],
       ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris" \
          or OS=="netbsd" or OS=="qnx" or OS=="aix"', {
         'conditions': [
           [ 'v8_no_strict_aliasing==1', {
             'cflags': [ '-fno-strict-aliasing' ],
           }],
         ],  # conditions
       }],
+      # GCC 6+ can optimize away pointer comparisons to null. This is
+      # problematic as V8 encodes Values through tagged pointers and comparisons
+      # with 0 are actually necessary in many cases. As a temporary Workaround
+      # we disable this optimization. See:
+      # https://bugs.chromium.org/p/v8/issues/detail?id=3782

[Michael Achenbach, 2016/09/05 06:53:39]

nit: short link: crbug.com/v8/3782

[ofrobots, 2016/09/07 00:36:39]

Done.

+      ['OS!="win" and clang==0', {
+        'cflags': [ '-fno-delete-null-pointer-checks' ]

[Michael Achenbach, 2016/09/05 06:53:39]

Please also add the GN configs as our bots testing this are about to switch or
already switched.

You'd need to add here:
https://cs.chromium.org/chromium/src/v8/BUILD.gn?l=194 (somewhere in
config("toolchain")) something like:

if (!is_win && !is_clang) {
  cflags += [ "-fno-delete-null-pointer-checks" ]
}

Then please also include trybots on the chromium side like
android_arm64_dbg_recipe.

[ofrobots, 2016/09/07 00:36:39]

Done.

+      }],
       ['OS=="solaris"', {
         'defines': [ '__C99FEATURES__=1' ],  # isinf() etc.
       }],
       ['OS=="freebsd" or OS=="openbsd"', {
         'cflags': [ '-I/usr/local/include' ],
       }],
       ['OS=="netbsd"', {
         'cflags': [ '-I/usr/pkg/include' ],
       }],
       ['OS=="aix"', {
@@ skipping 300 matching lines @@
             ],
           },
           'Release_x64': {
             'inherit_from': ['ReleaseBase'],
           },
         }],
       ],
     },  # configurations
   },  # target_defaults
 }