GN: build sfntly, icu, harfbuzz

gn/BUILDCONFIG.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # It's best to keep the names and defaults of is_foo flags consistent with Chrome.
 
 declare_args() {
   is_debug = true
   is_component_build = false
@@ skipping 22 matching lines @@
   if (is_component_build) {
     _component_mode = "shared_library"
   }
 
   target(_component_mode, target_name) {
     forward_variables_from(invoker, "*")
   }
 }
 
 # Default configs
-_default_configs = [ "//gn:default" ]
+default_configs = [
+  "//gn:default",
+  "//gn:no_rtti",
+]
 if (!is_debug) {
-  _default_configs += [ "//gn:release" ]
+  default_configs += [ "//gn:release" ]
 }
 
 set_defaults("executable") {
-  configs = _default_configs + [ "//gn:executable" ]
+  configs = default_configs + [ "//gn:executable" ]
 }
 
 set_defaults("source_set") {
-  configs = _default_configs
+  configs = default_configs
 }
 
 set_defaults("static_library") {
-  configs = _default_configs
+  configs = default_configs
 }
 
 set_defaults("shared_library") {
-  configs = _default_configs
+  configs = default_configs
 }
 
 set_defaults("component") {
-  configs = _default_configs
+  configs = default_configs
 }
 
 # For now, we support GCC-like toolchains, including Clang.
 set_default_toolchain("//gn:gcc_like")