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

gypfiles/toolchain.gypi

Index: gypfiles/toolchain.gypi
diff --git a/gypfiles/toolchain.gypi b/gypfiles/toolchain.gypi
index 95eb1d99cbff3f1172153e8652c02e6e83f82d7e..28265fbdf209c9bc1e18fa08d4cd3ac325e024b0 100644
--- a/gypfiles/toolchain.gypi
+++ b/gypfiles/toolchain.gypi
@@ -1098,6 +1098,14 @@
           }],
         ],  # 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.
       }],