Handle unpatched VS xtree header

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 7c06e5934c8c53a569df09179c8bfa5f0cd62ac5..e301a2791aecccd356cdb0943f593ecdf58d250f 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -356,6 +356,7 @@ _native_compiler_configs = [
 if (is_win) {
   _native_compiler_configs += [
     "//build/config/win:lean_and_mean",
+    "//build/config/win:msvs_xtree_unreachable_code",

[brettw, 2015/02/27 22:43:24]

We only need to add stuff to this list of targets need to opt-out of that
warning specifically. In this case, it looks like we want everybody to get this
flag.

We can instead add cflags = [ "/wd4702" ] to the
//build/config/compiler:default_warnings config to avoid this.

Also, since we don't need to share the xtree value with any other .gn files, we
can move the exec_script call to that file in an "if (is_win)" block.

Last, do we need to set this value from "gn args"? I can't think of any reason
why I would want to do this. In this case, we shouldn't put the variable in the
declare_args block and just use a normal file-local variable.

     "//build/config/win:nominmax",
     "//build/config/win:sdk",
     "//build/config/win:unicode",