Moves BUILD.gn config from root to runtime.

runtime/BUILD.gn

 # Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
+config("dart_config") {
+  defines = []
+  if (is_debug) {
+    defines += ["DEBUG"]
+  } else {
+    defines += ["NDEBUG"]
+  }
+
+  cflags = [
+    "-Werror",
+    "-Wall",
+    "-Wextra", # Also known as -W.
+    "-Wno-unused-parameter",
+    "-Wnon-virtual-dtor",
+    "-Wvla",
+    "-Wno-conversion-null",
+    "-Woverloaded-virtual",
+    "-g3",
+    "-ggdb3",
+    "-fno-rtti",
+    "-fno-exceptions",
+  ]
+}
+
+
 static_library("libdart") {
-  configs += ["..:dart_config"]
+  configs += [":dart_config"]
   deps = [
     "vm:libdart_lib",
     "vm:libdart_vm",
     "third_party/jscre:libjscre",
     "third_party/double-conversion/src:libdouble_conversion",
     ":generate_version_cc_file",
   ]
   include_dirs = [
     ".",
   ]
@@ skipping 43 matching lines @@
     "vm:libdart_lib",
     "vm:libdart_vm",
     "vm:libdart_platform",
     "third_party/jscre:libjscre",
     "third_party/double-conversion/src:libdouble_conversion",
   ]
   sources = [
     "vm/libdart_dependency_helper.cc",
   ]
 }